Sketch: accept redundant but consistent constraints (#687) (#699)

A clover of same-size rectangles drawn around a shared corner was refused as over-constrained. Constraints that remove no degree of freedom but still hold (zero residual) are now kept and shown dimmed as redundant. Conflicting ones are still refused. A redundant driving dimension is refused with "already determined by ...". Typed sizes become driven (reference) dimensions. Drawing no longer adds Horizontal/Vertical to a side that is already implied through two coincident corners. The solver reports redundant constraints using a Jacobian row-dependence test. Co-Authored-By: Claude Opus 5.5 <[email protected]>
2026-10-13 10:12:55 -04:00
1 parent add4a18961
commit 9ba72e118b
@@ -106,7 +106,7 @@ pub static COMMANDS: &[CommandSpec] = &[
        .params(concat!("p0, p1: overall ends, width", connect_doc!(), created_doc!())),
    CommandSpec::new("sketch.point", "Point", draw_point).at("SKETCH", "CREATE").icon("point").enabled(in_sketch).params(concat!("point: [x,y], id?", connect_doc!(), created_doc!())),
    CommandSpec::new("sketch.dimension", "Sketch Dimension", dimension).at("SKETCH", "CREATE").icon("dimension").key("D").enabled(in_sketch).params(
-        "entities: [refs], type?: auto|distance|horizontal|vertical|length|radius|diameter|angle, value?: number or expression (default: current; a bare number is in the design's units, e.g. 2 means 2 in in an inch design; give a unit such as \"50 mm\" to override); text_at?: [x, y]. Two points or a line off the axes: with auto, text_at across from them is the distance between them, above or below them horizontal, beside them vertical. Two lines: the angle between them (acute, or 180° − it when the value is nearer that) unless text_at picks a sector. Returns measured in unit (mm or deg)",
+        "entities: [refs], type?: auto|distance|horizontal|vertical|length|radius|diameter|angle, value?: number or expression (default: current; a bare number is in the design's units, e.g. 2 means 2 in in an inch design; give a unit such as \"50 mm\" to override); text_at?: [x, y]. Two points or a line off the axes: with auto, text_at across from them is the distance between them, above or below them horizontal, beside them vertical. Two lines: the angle between them (acute, or 180° − it when the value is nearer that) unless text_at picks a sector. A dimension the sketch already determines is refused (naming what determines it); if_redundant?: \"driven\" places it as a driven (reference) dimension instead. Returns measured in unit (mm or deg)",
    ),
    CommandSpec::new("sketch.constraint.horizontal_vertical", "Horizontal/Vertical", c_horizontal_vertical)
        .at("SKETCH", "CONSTRAINTS")
@@ -401,6 +401,7 @@ pub(super) fn draw(
        let first = sk.points.len();
        let (curves, mut cons) = f(sk, doc)?;
        cons.extend(connect_points(sk, first, p)?);
+        drop_implied_axes(sk, &mut cons);
        Ok((curves, cons))
    })
 }
@@ -821,6 +822,74 @@ fn rect_constraints(sk: &mut Sketch, l: &[usize]) -> Result<Vec<String>> {
    Ok(cons)
 }

+/// Whether line `l` being horizontal (`horizontal`) or vertical already follows from another
+/// constraint than `own`: its ends coincide with the ends of a line constrained the same way (a
+/// side two rectangles share), or with two points constrained level (or plumb).
+fn axis_implied(sk: &Sketch, l: usize, horizontal: bool, own: &str) -> bool {
+    let Some(CurveKind::Line { a, b }) = sk.curves.get(l).map(|c| &c.kind) else { return false };
+    let (a, b) = (*a, *b);
+    // Coincident points as one (union-find over the coincident constraints).
+    let mut parent: Vec<usize> = (0..sk.points.len()).collect();
+    let root = |parent: &[usize], mut i: usize| {
+        for _ in 0..parent.len() {
+            match parent.get(i) {
+                Some(&up) if up != i => i = up,
+                _ => break,
+            }
+        }
+        i
+    };
+    for c in &sk.constraints {
+        if let ConstraintKind::Coincident { p, q } = c.kind {
+            let (rp, rq) = (root(&parent, p), root(&parent, q));
+            if rp != rq
+                && let Some(slot) = parent.get_mut(rp)
+            {
+                *slot = rq;
+            }
+        }
+    }
+    let (ra, rb) = (root(&parent, a), root(&parent, b));
+    sk.constraints.iter().filter(|c| c.id != own).any(|c| {
+        let ends = match (&c.kind, horizontal) {
+            (ConstraintKind::Horizontal { l: m }, true) | (ConstraintKind::Vertical { l: m }, false) if *m != l => {
+                match sk.curves.get(*m).map(|c| &c.kind) {
+                    Some(CurveKind::Line { a, b }) => Some((*a, *b)),
+                    _ => None,
+                }
+            }
+            (ConstraintKind::HorizontalPoints { p, q }, true) | (ConstraintKind::VerticalPoints { p, q }, false) => Some((*p, *q)),
+            _ => None,
+        };
+        ends.is_some_and(|(p, q)| {
+            let (rp, rq) = (root(&parent, p), root(&parent, q));
+            rp != rq && ((rp, rq) == (ra, rb) || (rp, rq) == (rb, ra))
+        })
+    })
+}
+
+/// Drawing adds horizontal/vertical only where it is not already implied: a rectangle drawn
+/// onto another's side shares that side's direction through the two coincident corners, so a
+/// second "vertical" there would only be redundant. Drops such constraints among `cons` (the
+/// drawing's own) from the sketch and the list.
+fn drop_implied_axes(sk: &mut Sketch, cons: &mut Vec<String>) {
+    let mut dropped = Vec::new();
+    for id in cons.iter() {
+        let axis = sk.constraints.iter().find(|c| &c.id == id).and_then(|c| match c.kind {
+            ConstraintKind::Horizontal { l } => Some((l, true)),
+            ConstraintKind::Vertical { l } => Some((l, false)),
+            _ => None,
+        });
+        if let Some((l, horizontal)) = axis
+            && axis_implied(sk, l, horizontal, id)
+        {
+            sk.constraints.retain(|c| &c.id != id);
+            dropped.push(id.clone());
+        }
+    }
+    cons.retain(|id| !dropped.contains(id));
+}
+
 /// Which side and corner of an axis-aligned rectangle is which, from its lines and corner
 /// points as `polygon_lines` made them (counter-clockwise from the bottom-left corner), so a
 /// caller can dimension it without inspecting the sketch first.
@@ -855,6 +924,7 @@ fn rect_two_point(s: &mut Session, p: &Value) -> Result<Value> {
        let mut cons = rect_constraints(sk, &l)?;
        mark_construction(sk, &l, p);
        cons.extend(connect_points(sk, first, p)?);
+        drop_implied_axes(sk, &mut cons);
        Ok(((ids_of(sk, &l), cons), rect_names(sk, &l, &pts)))
    })?;
    Ok(rect_result(out, names, info))
@@ -887,6 +957,7 @@ fn rect_center(s: &mut Session, p: &Value) -> Result<Value> {
        }
        mark_construction(sk, &l, p);
        cons.extend(connect_points(sk, first, p)?);
+        drop_implied_axes(sk, &mut cons);
        Ok(((ids_of(sk, &l), cons), rect_names(sk, &l, &pts)))
    })?;
    Ok(rect_result(out, names, info))
@@ -1174,19 +1245,24 @@ fn draw_point(s: &mut Session, p: &Value) -> Result<Value> {

 fn constrain(s: &mut Session, p: &Value, cmd: &str, f: impl FnOnce(&mut Sketch) -> Result<ConstraintKind>) -> Result<Value> {
    let mut before = None;
+    let mut residual = None;
    let (id, info) = edit(s, p, cmd, true, |sk, _| {
        let k = f(sk)?;
        let rep = solve(&mut sk.clone());
        before = Some(rep.dof);
        let order = entity_order(sk, p);
        let id = add_c(sk, k)?;
-        if let Some((first, second)) = order {
+        residual = residual_of(sk, &id);
+        // A constraint that already holds needs nothing moved (even when both entities are
+        // fully determined: it is then redundant, see `redundancy`).
+        let holds = residual.is_some_and(|r| r <= solidcraft_sketch::CONSISTENT);
+        if let Some((first, second)) = order.filter(|_| !holds) {
            apply_in_order(sk, &rep, &[first], second, cmd)?;
        }
        Ok(id)
    })?;
-    reject_redundant(before, &info, cmd)?;
-    Ok(json!({"constraint": id, "sketch": info}))
+    let by = redundancy(s, p, cmd, before, &info, residual, &id)?;
+    constraint_result(p, cmd, id, info, by, Value::Null)
 }

 /// A sketch entity a constraint is applied to.
@@ -1330,18 +1406,79 @@ pub(super) fn dof_now(sk: &Sketch) -> usize {
    solve(&mut sk.clone()).dof
 }

-/// A constraint that removes no degree of freedom over-constrains the sketch (Fusion refuses
-/// it); the caller's edit is rolled back by returning the error.
-pub(super) fn reject_redundant(before: Option<usize>, info: &Value, cmd: &str) -> Result<()> {
+/// A constraint just added that removes no degree of freedom (`before` → the edit's `info`) is
+/// redundant or a conflict. Redundant when it held where the sketch was before it was added
+/// (`residual`, see [`solidcraft_sketch::constraint_residual`]): what it asks for is already
+/// implied by other constraints, and the solver satisfies it with them. Returns the
+/// constraints that determine it (as "id (Name)"), or `None` when it removes a degree of
+/// freedom. A conflict is refused; the caller's edit is rolled back by returning the error.
+pub(super) fn redundancy(
+    s: &Session,
+    p: &Value,
+    cmd: &str,
+    before: Option<usize>,
+    info: &Value,
+    residual: Option<f64>,
+    cid: &str,
+) -> Result<Option<Vec<String>>> {
    let after = info.get("dof").and_then(Value::as_u64).map(|d| d as usize);
-    if let (Some(b), Some(a)) = (before, after)
-        && a >= b
-    {
-        return Err(bad(cmd, "that would over-constrain the sketch (it is already determined by other constraints)"));
+    let (Some(b), Some(a)) = (before, after) else { return Ok(None) };
+    if a < b {
+        return Ok(None);
+    }
+    if !residual.is_some_and(|r| r <= solidcraft_sketch::CONSISTENT) {
+        return Err(bad(cmd, "that would over-constrain the sketch (it conflicts with what the other constraints already determine)"));
+    }
+    Ok(Some(determined_by(s, p, cmd, cid)))
+}
+
+/// The constraints that already determine constraint `cid` of the target sketch, as
+/// "id (Name)".
+fn determined_by(s: &Session, p: &Value, cmd: &str, cid: &str) -> Vec<String> {
+    let Some(sk) = target_sketch(s, p, cmd).ok().and_then(|id| s.doc.sketch(id).ok()) else { return Vec::new() };
+    let Some(ci) = sk.constraints.iter().position(|c| c.id == cid) else { return Vec::new() };
+    solidcraft_sketch::determined_by(sk, ci)
+        .into_iter()
+        .filter_map(|k| sk.constraints.get(k))
+        .map(|c| format!("{} ({})", c.id, c.kind.name()))
+        .collect()
+}
+
+/// "k3 (Vertical), k9 (Vertical)", or "other constraints" when they are not known.
+pub(super) fn listed(by: &[String]) -> String {
+    if by.is_empty() { "other constraints".to_string() } else { by.join(", ") }
+}
+
+/// A redundant constraint is kept (and shown as redundant) unless the caller asked for
+/// `if_redundant: "refuse"` (drawing-time inferences, which only add what is not already there).
+pub(super) fn keep_redundant(p: &Value, cmd: &str, by: &[String]) -> Result<()> {
+    if str_(p, "if_redundant").is_some_and(|m| m.eq_ignore_ascii_case("refuse")) {
+        return Err(bad(cmd, format!("that would over-constrain the sketch (it is already determined by {})", listed(by))));
    }
    Ok(())
 }

+/// The result of a constraint command: the constraint, and whether it is redundant (and what
+/// determines it).
+pub(super) fn constraint_result(p: &Value, cmd: &str, id: String, info: Value, by: Option<Vec<String>>, extra: Value) -> Result<Value> {
+    let mut out = json!({"constraint": id, "sketch": info});
+    if let Some(by) = by {
+        keep_redundant(p, cmd, &by)?;
+        out["redundant"] = json!(true);
+        out["determined_by"] = json!(by);
+    }
+    if let (Some(o), Value::Object(e)) = (out.as_object_mut(), extra) {
+        o.extend(e);
+    }
+    Ok(out)
+}
+
+/// The residual of the constraint `id` where the sketch is now (see
+/// [`solidcraft_sketch::constraint_residual`]).
+pub(super) fn residual_of(sk: &Sketch, id: &str) -> Option<f64> {
+    sk.constraints.iter().position(|c| c.id == id).and_then(|ci| solidcraft_sketch::constraint_residual(sk, ci))
+}
+
 fn c_horizontal_vertical(s: &mut Session, p: &Value) -> Result<Value> {
    let cmd = "sketch.constraint.horizontal_vertical";
    let mode = str_(p, "mode").map(str::to_ascii_lowercase);
@@ -1610,6 +1747,8 @@ fn dimension(s: &mut Session, p: &Value) -> Result<Value> {
    let text_at = p.get("text_at").and_then(vec2);
    let driven = bool_(p, "driven").unwrap_or(false);
    let mut before = None;
+    let (mut residual, mut new_id) = (None, String::new());
+    let start = s.doc.clone();
    let ((param, kind_name, current), info) = edit(s, p, cmd, true, |sk, doc| {
        before = Some(dof_now(sk));
        let ent = |r: &str| -> Result<(Option<usize>, Option<usize>)> {
@@ -1766,8 +1905,13 @@ fn dimension(s: &mut Session, p: &Value) -> Result<Value> {
        {
            (k, cur) = (ka, ca);
        }
+        // How far the value is from what the geometry measures now: zero for a dimension that
+        // only restates what the sketch already has.
+        let want = vals.get(&pname).and_then(|v| v.to_kind(if is_angle { Kind::Angle } else { Kind::Length }).ok());
+        residual = want.map(|w| (w - cur).abs()).filter(|r| r.is_finite());
        let name = k.name();
        let id = sk.add_constraint(k, Some(pname.clone()))?;
+        new_id = id.clone();
        place_text(sk, &id, text_at);
        Ok((pname, name, measured(is_angle, cur)))
    })?;
@@ -1776,8 +1920,28 @@ fn dimension(s: &mut Session, p: &Value) -> Result<Value> {
    if driven {
        return Ok(json!({"param": Value::Null, "driven": true, "type": kind_name, "measured": current.0, "unit": current.1, "sketch": info}));
    }
-    if reject_redundant(before, &info, cmd).is_err() {
-        return Err(bad(cmd, "that dimension would over-constrain the sketch; add it as a driven (reference) dimension with driven: true"));
+    // A dimension the sketch already determines cannot drive it: it is refused, or with
+    // `if_redundant: "driven"` placed as a driven (reference) dimension instead.
+    let by = redundancy(s, p, cmd, before, &info, residual, &new_id)
+        .map_err(|_| bad(cmd, "that dimension conflicts with the sketch: other constraints already determine it with a different value"))?;
+    if let Some(by) = by {
+        if str_(p, "if_redundant").is_some_and(|m| m.eq_ignore_ascii_case("driven")) {
+            s.doc = start;
+            let mut q = p.clone();
+            q["driven"] = json!(true);
+            if let Some(o) = q.as_object_mut() {
+                o.remove("if_redundant");
+                o.remove("value");
+            }
+            let mut out = dimension(s, &q)?;
+            out["redundant"] = json!(true);
+            out["determined_by"] = json!(by);
+            return Ok(out);
+        }
+        return Err(bad(
+            cmd,
+            format!("that dimension is already determined by {}; add it as a driven (reference) dimension with driven: true", listed(&by)),
+        ));
    }
    let v = s.doc.param(&param).map(|p| p.expr.clone()).unwrap_or_default();
    Ok(json!({"param": param, "type": kind_name, "expression": v, "measured": current.0, "unit": current.1, "sketch": info}))
@@ -2156,3 +2320,6 @@ mod drag_live_tests;
 #[cfg(test)]
 #[path = "sketch_ids_tests.rs"]
 mod ids_tests;
+#[cfg(test)]
+#[path = "sketch_redundant_tests.rs"]
+mod redundant_tests;
@@ -232,7 +232,8 @@ fn bad_line_references_are_errors_and_change_nothing() {
    // A constraint the sketch refuses rolls the axis line back with it.
    run(&mut s, "sketch.constraint.horizontal_vertical", json!({"line": "b", "mode": "horizontal"}));
    let before_redundant = s.doc.to_json();
-    assert!(s.execute("sketch.constraint.parallel", &json!({"a": "b", "b": "x"})).is_err(), "already horizontal");
+    // (A redundant one is kept unless refused: refused here.)
+    assert!(s.execute("sketch.constraint.parallel", &json!({"a": "b", "b": "x", "if_redundant": "refuse"})).is_err(), "already horizontal");
    assert_eq!(s.doc.to_json(), before_redundant);
    assert!(axis_lines(&sketch(&s)).is_empty());
 }
@@ -5,7 +5,7 @@ use serde_json::{Value, json};
 use solidcraft_geom::Vec2;
 use solidcraft_sketch::{ConstraintKind, CurveKind, Sketch};

-use super::sketch::{add_c, dof_now, edit, reject_redundant};
+use super::sketch::{add_c, constraint_result, dof_now, edit, listed, redundancy, residual_of};
 use super::{CommandSpec, in_sketch};
 use crate::params::{bad, num, req_vec2, str_, string_list, vec2};
 use crate::{EngineError, Result, Session};
@@ -56,15 +56,17 @@ pub static COMMANDS: &[CommandSpec] = &[

 fn c_smooth(s: &mut Session, p: &Value) -> Result<Value> {
    let cmd = "sketch.constraint.curvature";
-    let mut before = None;
+    let (mut before, mut residual) = (None, None);
    let (id, info) = edit(s, p, cmd, true, |sk, _| {
        let a = curve(sk, p.get("a"), cmd)?;
        let b = curve(sk, p.get("b"), cmd)?;
        before = Some(dof_now(sk));
-        add_c(sk, ConstraintKind::Smooth { a, b })
+        let id = add_c(sk, ConstraintKind::Smooth { a, b })?;
+        residual = residual_of(sk, &id);
+        Ok(id)
    })?;
-    reject_redundant(before, &info, cmd)?;
-    Ok(json!({"constraint": id, "sketch": info}))
+    let by = redundancy(s, p, cmd, before, &info, residual, &id)?;
+    constraint_result(p, cmd, id, info, by, Value::Null)
 }

 fn curve(sk: &Sketch, v: Option<&Value>, cmd: &str) -> Result<usize> {
@@ -349,16 +351,18 @@ fn guess(sk: &Sketch, ents: &[String], cmd: &str) -> Result<ConstraintKind> {
 fn smart_constrain(s: &mut Session, p: &Value) -> Result<Value> {
    let cmd = "sketch.constrainer";
    let ents = string_list(p, "entities");
-    let mut before = None;
+    let (mut before, mut residual) = (None, None);
    let mut name = "";
    let (id, info) = edit(s, p, cmd, true, |sk, _| {
        let k = guess(sk, &ents, cmd)?;
        name = k.name();
        before = Some(dof_now(sk));
-        add_c(sk, k)
+        let id = add_c(sk, k)?;
+        residual = residual_of(sk, &id);
+        Ok(id)
    })?;
-    reject_redundant(before, &info, cmd)?;
-    Ok(json!({"constraint": id, "type": name, "sketch": info}))
+    let by = redundancy(s, p, cmd, before, &info, residual, &id)?;
+    constraint_result(p, cmd, id, info, by, json!({"type": name}))
 }

 fn toggle_driven(s: &mut Session, p: &Value) -> Result<Value> {
@@ -397,7 +401,10 @@ fn toggle_driven(s: &mut Session, p: &Value) -> Result<Value> {
            c.driven = true;
        }
        before = Some(dof_now(&sk));
-        reject_redundant(before, &info, cmd)?;
+        // It holds (its parameter takes the value it measures), so it can only be redundant.
+        if let Some(by) = redundancy(s, p, cmd, before, &info, Some(0.0), &cid)? {
+            return Err(bad(cmd, format!("that dimension is already determined by {}; it stays driven", listed(&by))));
+        }
    }
    s.doc_mut().prune_model_params();
    Ok(json!({"constraint": cid, "driven": driven, "sketch": info}))
@@ -468,6 +475,8 @@ fn glyphs(s: &mut Session, p: &Value) -> Result<Value> {
                "param": c.param,
                "at": anchor(&ss.sketch, &c.kind),
                "failing": failing.contains(&c.id),
+                // Implied by the others (it removes no freedom) but holding: shown dimmed.
+                "redundant": ss.report.redundant.contains(&c.id),
            })
        })
        .collect();
@@ -25,17 +25,17 @@ fn sketch(s: &Session) -> solidcraft_sketch::Sketch {
 }

 #[test]
-fn redundant_constraints_and_dimensions_are_refused_driven_ones_measure() {
+fn redundant_dimensions_are_refused_driven_ones_measure() {
    let mut s = new_sketch();
    let l = ids(&run(&mut s, "sketch.line", json!({"points": [[0, 0], [10, 0]], "infer": true}))["curves"])[0].clone();
-    // Already horizontal (inferred).
-    let e = s.execute("sketch.constraint.horizontal_vertical", &json!({"line": l})).unwrap_err().to_string();
-    assert!(e.contains("over-constrain"), "{e}");
+    // Already horizontal (inferred): kept as redundant, unless asked to refuse it.
+    let e = s.execute("sketch.constraint.horizontal_vertical", &json!({"line": l, "if_redundant": "refuse"})).unwrap_err().to_string();
+    assert!(e.contains("over-constrain") && e.contains("already determined by"), "{e}");
    run(&mut s, "sketch.constraint.coincident", json!({"a": format!("{l}.start"), "b": "origin"}));
    run(&mut s, "sketch.dimension", json!({"entities": [l], "value": 10}));
    let si = run(&mut s, "sketch.inspect", json!({}));
    assert_eq!(si["dof"], 0, "{si}");
-    // A second length on it over-constrains: refused, unless driven.
+    // A second length on it is already determined: refused, unless driven.
    assert!(s.execute("sketch.dimension", &json!({"entities": [format!("{l}.start"), format!("{l}.end")]})).is_err());
    let d = run(&mut s, "sketch.dimension", json!({"entities": [format!("{l}.start"), format!("{l}.end")], "driven": true}));
    assert_eq!(d["driven"], true);
@@ -95,7 +95,9 @@ pub(super) fn draw(s: &mut Session, p: &Value) -> Result<Value> {
            }
            _ => return Err(bad(cmd, "unsupported dimension role")),
        };
-        let mut dimension = json!({"entities": entities, "type": ty, "value": value});
+        // A typed size the sketch already has (a rectangle drawn onto another's side, the same
+        // height) is placed as a driven (reference) dimension rather than refused.
+        let mut dimension = json!({"entities": entities, "type": ty, "value": value, "if_redundant": "driven"});
        if let Some(sketch) = params.get("sketch") {
            dimension["sketch"] = sketch.clone();
        }
@@ -0,0 +1,252 @@
+//! Redundant but consistent constraints (#687): rectangles of one size drawn around a shared
+//! corner (a "clover"), or onto each other's sides, imply some of their constraints twice. Those
+//! are kept (and reported as redundant) or not added at all; only constraints that conflict
+//! with the sketch are refused.
+
+use serde_json::{Value, json};
+use solidcraft_geom::Vec2;
+
+use crate::Session;
+
+fn run(s: &mut Session, id: &str, p: Value) -> Value {
+    match s.execute(id, &p) {
+        Ok(v) => v,
+        Err(e) => panic!("{id} {p}: {e}"),
+    }
+}
+
+fn new_sketch() -> Session {
+    let mut s = Session::default();
+    run(&mut s, "sketch.create", json!({"plane": "XY"}));
+    s
+}
+
+fn sketch(s: &Session) -> solidcraft_sketch::Sketch {
+    s.model.state().sketch(s.active_sketch.unwrap()).unwrap().sketch.clone()
+}
+
+fn report(s: &Session) -> solidcraft_sketch::SolveReport {
+    s.model.state().sketch(s.active_sketch.unwrap()).unwrap().report.clone()
+}
+
+fn glyphs(s: &mut Session) -> Value {
+    run(s, "sketch.glyphs", json!({}))
+}
+
+/// The four quadrants around `c`, each `w` square: bottom-left, bottom-right, top-right,
+/// top-left (each next one shares a side with the one before; the last shares two).
+fn quadrants(c: [f64; 2], w: f64) -> [([f64; 2], [f64; 2]); 4] {
+    let [x, y] = c;
+    [([x - w, y - w], [x, y]), ([x, y - w], [x + w, y]), ([x, y], [x + w, y + w]), ([x - w, y], [x, y + w])]
+}
+
+fn horizontal_vertical(sk: &solidcraft_sketch::Sketch) -> usize {
+    sk.constraints
+        .iter()
+        .filter(|c| matches!(c.kind, solidcraft_sketch::ConstraintKind::Horizontal { .. } | solidcraft_sketch::ConstraintKind::Vertical { .. }))
+        .count()
+}
+
+/// The owner's steps: rectangles of one size (typed 10 × 10) drawn snapped onto a shared
+/// corner, 2, 3 and 4 of them. Every one is accepted; a size the sketch already has becomes a
+/// driven (reference) dimension, and the sketch ends fully constrained.
+#[test]
+fn a_clover_of_same_size_rectangles_drawn_by_snapping_is_accepted() {
+    for n in 2..=4 {
+        let mut s = new_sketch();
+        for (i, (a, b)) in quadrants([0.0, 0.0], 10.0).iter().take(n).enumerate() {
+            let r = s.execute(
+                "sketch.draw.dimensioned",
+                &json!({"command": "sketch.rectangle.two_point", "params": {"p0": a, "p1": b}, "dimensions": {"width": 10, "height": 10}}),
+            );
+            let r = r.unwrap_or_else(|e| panic!("rectangle {i} of {n}: {e}"));
+            assert_eq!(r["sketch"]["solved"], true, "{r}");
+        }
+        let g = glyphs(&mut s);
+        assert_eq!(g["fully_constrained"], true, "{n} rectangles: {g}");
+        assert_eq!(g["conflicts"], json!([]), "{g}");
+        let sk = sketch(&s);
+        assert_eq!(sk.curves.len(), 4 * n);
+        // Shared sides carry one horizontal/vertical, not two: 4 for the first rectangle, 3 for
+        // each with one shared side, 2 for the last of four (two shared sides).
+        let expected = [0, 4, 7, 10, 12][n];
+        assert_eq!(horizontal_vertical(&sk), expected, "{n} rectangles");
+        // Each later rectangle's size along a shared side is a reference dimension.
+        let driven = sk.constraints.iter().filter(|c| c.driven).count();
+        assert_eq!(driven, [0, 0, 1, 2, 4][n], "{n} rectangles");
+        for (a, b) in quadrants([0.0, 0.0], 10.0).iter().take(n) {
+            for corner in [Vec2::new(a[0], a[1]), Vec2::new(b[0], b[1])] {
+                assert!(sk.points.iter().any(|p| p.pos.dist(corner) < 1e-9), "{n} rectangles: corner {corner:?} moved");
+            }
+        }
+    }
+}
+
+/// Undimensioned, the same clover is drawn without a single redundant constraint: shared
+/// sides are not constrained twice, and the freedom left is the two column widths and the two
+/// row heights.
+#[test]
+fn rectangles_sharing_sides_do_not_constrain_a_side_twice() {
+    let mut s = new_sketch();
+    for (a, b) in quadrants([50.0, 50.0], 10.0) {
+        run(&mut s, "sketch.rectangle.two_point", json!({"p0": a, "p1": b}));
+    }
+    let rep = report(&s);
+    assert!(rep.ok(), "{rep:?}");
+    assert_eq!(rep.redundant, Vec::<String>::new());
+    // Free: the shared corner (2), two column widths, two row heights.
+    assert_eq!(rep.dof, 6);
+    assert_eq!(horizontal_vertical(&sketch(&s)), 12);
+}
+
+/// Two rectangles on one side: the second only adds its width.
+#[test]
+fn shared_edge_rectangles() {
+    let mut s = new_sketch();
+    run(&mut s, "sketch.rectangle.two_point", json!({"p0": [0, 0], "p1": [10, 10]}));
+    let r = run(&mut s, "sketch.rectangle.two_point", json!({"p0": [10, 0], "p1": [25, 10]}));
+    // Three of its sides' directions and its two corners on the first one.
+    assert_eq!(r["constraints"].as_array().map(Vec::len), Some(5), "{r}");
+    let rep = report(&s);
+    assert_eq!(rep.dof, 3, "the first one's width and height, the second one's width");
+    assert!(rep.redundant.is_empty());
+    // Sized and placed, all of it is fixed.
+    run(&mut s, "sketch.dimension", json!({"entities": ["l1"], "value": 10}));
+    run(&mut s, "sketch.dimension", json!({"entities": ["l2"], "value": 10}));
+    run(&mut s, "sketch.dimension", json!({"entities": ["l5"], "value": 15}));
+    assert_eq!(glyphs(&mut s)["fully_constrained"], true);
+}
+
+/// Two separately drawn 10 × 10 squares snapped corner to corner: the second snap is implied by
+/// the first and the equal sizes. It is kept, reported as redundant along with what implies
+/// it, and the degrees of freedom and the fully constrained state are unchanged.
+#[test]
+fn snapping_a_second_corner_of_same_size_rectangles_is_redundant_not_refused() {
+    let mut s = new_sketch();
+    for (a, b) in [([0.0, 0.0], [10.0, 10.0]), ([20.0, 0.0], [30.0, 10.0])] {
+        run(
+            &mut s,
+            "sketch.draw.dimensioned",
+            json!({"command": "sketch.rectangle.two_point", "params": {"p0": a, "p1": b}, "dimensions": {"width": 10, "height": 10}}),
+        );
+    }
+    // The second square's bottom-left corner onto the first one's bottom-right.
+    run(&mut s, "sketch.constraint.coincident", json!({"a": "l5.start", "b": "l1.end"}));
+    let dof = report(&s).dof;
+    assert_eq!(dof, 0, "the first square is on the origin, the second one placed by its corner");
+    // Its top-left corner is already on the first one's top-right.
+    let r = run(&mut s, "sketch.constraint.coincident", json!({"a": "l7.end", "b": "l2.end"}));
+    assert_eq!(r["redundant"], true, "{r}");
+    assert!(!r["determined_by"].as_array().is_none_or(Vec::is_empty), "{r}");
+    let rep = report(&s);
+    assert_eq!((rep.ok(), rep.dof), (true, 0));
+    assert_eq!(rep.redundant, vec![r["constraint"].as_str().unwrap().to_string()]);
+    let g = glyphs(&mut s);
+    assert_eq!(g["fully_constrained"], true);
+    let flagged: Vec<&Value> = g["glyphs"].as_array().unwrap().iter().filter(|x| x["redundant"] == true).collect();
+    assert_eq!(flagged.len(), 1, "{g}");
+    // Drawing-time inferences ask for redundant ones to be left out.
+    let e = s.execute("sketch.constraint.horizontal_vertical", &json!({"line": "l8", "if_redundant": "refuse"})).unwrap_err().to_string();
+    assert!(e.contains("already determined by"), "{e}");
+}
+
+/// A size the sketch already has, dimensioned again: refused as already determined (naming
+/// what determines it), or placed as a driven dimension; an equal constraint the sketch already
+/// implies is kept as redundant.
+#[test]
+fn redundant_equal_dimensions() {
+    let mut s = new_sketch();
+    run(&mut s, "sketch.rectangle.two_point", json!({"p0": [0, 0], "p1": [10, 10]}));
+    run(&mut s, "sketch.rectangle.two_point", json!({"p0": [10, 0], "p1": [20, 10]}));
+    let height = run(&mut s, "sketch.dimension", json!({"entities": ["l2"], "value": 10}));
+    let k = sketch(&s).constraints.iter().find(|c| c.param.as_deref() == height["param"].as_str()).map(|c| c.id.clone()).unwrap();
+    // The second one's right side is as tall as the shared side.
+    let e = s.execute("sketch.dimension", &json!({"entities": ["l6"], "value": 10})).unwrap_err().to_string();
+    assert!(e.contains("already determined by") && e.contains(&k), "{e}");
+    let d = run(&mut s, "sketch.dimension", json!({"entities": ["l6"], "value": 10, "if_redundant": "driven"}));
+    assert_eq!((d["driven"].clone(), d["redundant"].clone()), (json!(true), json!(true)), "{d}");
+    // Equal widths, twice: the second is implied by the first.
+    run(&mut s, "sketch.constraint.equal", json!({"a": "l1", "b": "l5"}));
+    let before = report(&s).dof;
+    let r = run(&mut s, "sketch.constraint.equal", json!({"a": "l3", "b": "l7"}));
+    assert_eq!(r["redundant"], true, "{r}");
+    assert_eq!(report(&s).dof, before);
+    // Its driving value changes still solve with the redundant constraints present.
+    let pname = height["param"].as_str().unwrap().to_string();
+    run(&mut s, "parameters.change", json!({"name": pname, "expression": "14 mm"}));
+    let sk = sketch(&s);
+    assert!(report(&s).ok());
+    let len = |id: &str| {
+        let c = sk.curve_index(id).unwrap();
+        let solidcraft_sketch::CurveKind::Line { a, b } = sk.curves[c].kind else { panic!() };
+        sk.points[a].pos.dist(sk.points[b].pos)
+    };
+    assert!((len("l6") - 14.0).abs() < 1e-7 && (len("l4") - 14.0).abs() < 1e-7);
+}
+
+/// A constraint that does not hold where the others put the geometry still conflicts.
+#[test]
+fn a_conflicting_constraint_is_still_refused() {
+    let mut s = new_sketch();
+    run(&mut s, "sketch.rectangle.two_point", json!({"p0": [0, 0], "p1": [10, 10]}));
+    run(&mut s, "sketch.rectangle.two_point", json!({"p0": [10, 0], "p1": [20, 10]}));
+    run(&mut s, "sketch.dimension", json!({"entities": ["l2"], "value": 10}));
+    let before = sketch(&s).constraints.len();
+    // The second one's right side cannot be 12 while the shared side is 10.
+    let e = s.execute("sketch.dimension", &json!({"entities": ["l6"], "value": 12})).unwrap_err().to_string();
+    assert!(e.contains("over-constrain") || e.contains("conflicts"), "{e}");
+    let e = s.execute("sketch.dimension", &json!({"entities": ["l6"], "value": 12, "if_redundant": "driven"})).unwrap_err().to_string();
+    assert!(e.contains("over-constrain") || e.contains("conflicts"), "{e}");
+    // A vertical side cannot be horizontal.
+    let e = s.execute("sketch.constraint.horizontal_vertical", &json!({"line": "l2", "mode": "horizontal"})).unwrap_err().to_string();
+    assert!(e.contains("over-constrain"), "{e}");
+    assert_eq!(sketch(&s).constraints.len(), before);
+    assert!(report(&s).redundant.is_empty());
+}
+
+/// Dragging the shared corner of a clover moves all four rectangles with it, redundant
+/// constraints and all.
+#[test]
+fn dragging_the_shared_corner_moves_every_rectangle() {
+    let mut s = new_sketch();
+    for (a, b) in quadrants([50.0, 50.0], 10.0) {
+        run(&mut s, "sketch.rectangle.two_point", json!({"p0": a, "p1": b}));
+    }
+    // A redundant equal and a redundant vertical, so the drag has some to carry.
+    run(&mut s, "sketch.constraint.equal", json!({"a": "l1", "b": "l13"}));
+    let r = run(&mut s, "sketch.constraint.horizontal_vertical", json!({"line": "l4"}));
+    assert_eq!(r["redundant"], true, "{r}");
+    assert!(!report(&s).redundant.is_empty());
+    let centre = Vec2::new(50.0, 50.0);
+    let id = sketch(&s).points.iter().find(|p| p.pos.dist(centre) < 1e-9).map(|p| p.id.clone()).unwrap();
+    run(&mut s, "sketch.drag", json!({"entity": id, "from": [50, 50], "to": [56, 47]}));
+    let sk = sketch(&s);
+    let rep = report(&s);
+    assert!(rep.ok(), "{rep:?}");
+    let to = Vec2::new(56.0, 47.0);
+    // Each rectangle still has a corner on the moved one and is still a rectangle.
+    let near: usize = sk.points.iter().filter(|p| p.pos.dist(to) < 1e-6).count();
+    assert!(near >= 4, "{near} corners at the dragged spot");
+    for l in &sk.curves {
+        let solidcraft_sketch::CurveKind::Line { a, b } = l.kind else { continue };
+        let d = sk.points[b].pos - sk.points[a].pos;
+        assert!(d.x.abs() < 1e-7 || d.y.abs() < 1e-7, "{} is no longer axis-aligned: {d:?}", l.id);
+    }
+    assert!(sk.points.iter().all(|p| p.pos.dist(centre) > 1e-6), "nothing stayed behind at the old corner");
+}
+
+/// A horizontal on a line that already is (it was drawn so, inferred) is redundant, not an
+/// error; the degrees of freedom do not change, and the sketch still turns fully constrained.
+#[test]
+fn an_explicit_redundant_constraint_keeps_the_dof_and_full_constraint() {
+    let mut s = new_sketch();
+    let l = run(&mut s, "sketch.line", json!({"points": [[0, 0], [10, 0]], "infer": true}))["curves"][0].as_str().unwrap().to_string();
+    let r = run(&mut s, "sketch.constraint.horizontal_vertical", json!({"line": l}));
+    assert_eq!(r["redundant"], true, "{r}");
+    // Its start is on the origin (snapped): only its length is free.
+    assert_eq!(report(&s).dof, 1);
+    run(&mut s, "sketch.dimension", json!({"entities": [l], "value": 10}));
+    let g = glyphs(&mut s);
+    assert_eq!((g["dof"].clone(), g["fully_constrained"].clone()), (json!(0), json!(true)), "{g}");
+    assert!(report(&s).point_determined.iter().all(|d| *d));
+}
@@ -55,8 +55,8 @@ pub use profiles::{
 };
 pub use shape::{Shape, intersections};
 pub use solver::{
-    Analysis, DrivingValues, Hold, SolveReport, SolveStatus, measure_dimension, solve, solve_after_edit, solve_after_value_edit, solve_holding,
-    solve_with,
+    Analysis, CONSISTENT, DrivingValues, Hold, SolveReport, SolveStatus, constraint_residual, determined_by, measure_dimension, solve,
+    solve_after_edit, solve_after_value_edit, solve_holding, solve_with,
 };
 pub use text::{MAX_TEXT_CHARS, text_geometry, text_geometry_in};
 pub use wire::{MAX_FIT_POINTS, MAX_WIRE_POINTS, Wire, WireSpace, fit_polyline};
@@ -0,0 +1,171 @@
+//! Redundant constraints: ones whose equations are already implied by the others where the
+//! sketch is now (two rectangles sharing a side both say the side is vertical; a coincidence
+//! between two corners that equal sizes already put together). They remove no degree of freedom
+//! but they do not conflict either: the solver satisfies them along with the rest.
+//!
+//! The test is the Jacobian's: walking the rows in order (the curves' own relations, then the
+//! constraints in the order they were added), a row that adds no rank to the rows before it is
+//! dependent on them. A constraint none of whose rows add rank is redundant. Whether a
+//! redundant constraint is consistent is a question of its residual (see
+//! [`constraint_residual`]): zero where the other constraints hold means it is implied, not in
+//! conflict.
+
+use super::{Block, Hold, Layout, State, block_residuals, build_blocks, columns, initial_x, layout, local_system, max_abs, points_on_curves};
+use crate::linalg::{Mat, solve as lin_solve};
+use crate::model::Sketch;
+use crate::union_find::{find, union};
+
+/// A row is dependent on the rows before it when what is left of it, once their directions are
+/// taken out, is below this share of its length (the rank analysis' pivot tolerance is 1e-7 on
+/// rows of a comparable scale).
+const DEPENDENT: f64 = 1e-6;
+/// Variables in one component past which its constraints are not checked for redundancy: the
+/// check is dense, rows × rank × variables.
+pub(super) const MAX_REDUNDANCY_VARS: usize = 400;
+/// A constraint's residual (mm, or radians for angles) below which it holds.
+pub const CONSISTENT: f64 = 1e-6;
+
+/// The constraint a block stands for.
+pub(super) fn block_constraint(b: &Block) -> Option<usize> {
+    match b {
+        Block::User(ci, _) | Block::TangentAt(ci, _, _) => Some(*ci),
+        Block::Closure { .. } | Block::Arc { .. } => None,
+    }
+}
+
+fn dot(a: &[f64], b: &[f64]) -> f64 {
+    a.iter().zip(b).map(|(x, y)| x * y).sum()
+}
+
+/// Per block of `blocks` (in order, over the variables `vars`): whether every one of its rows
+/// is a combination of the rows before it. With `support`, also for the block at that index
+/// (when redundant) the earlier blocks its rows combine.
+pub(super) fn dependent_blocks(
+    sk: &Sketch,
+    lay: &Layout,
+    blocks: &[(Block, Vec<usize>)],
+    vars: &[usize],
+    x: &mut [f64],
+    support: Option<usize>,
+) -> (Vec<bool>, Vec<usize>) {
+    let mut col = vec![usize::MAX; lay.n];
+    columns(&mut col, vars, vars);
+    let (_, j, owner) = local_system(sk, lay, blocks, x, &col, vars.len());
+    let n = j.cols;
+    let row = |k: usize| -> Vec<f64> { j.data.get(k * n..(k + 1) * n).map(<[f64]>::to_vec).unwrap_or_default() };
+    // Orthonormal directions of the independent rows so far, and those rows with their block.
+    let mut q: Vec<Vec<f64>> = Vec::new();
+    let mut basis: Vec<(Vec<f64>, usize)> = Vec::new();
+    let mut has_rows = vec![false; blocks.len()];
+    let mut adds_rank = vec![false; blocks.len()];
+    let mut target_rows: Vec<Vec<f64>> = Vec::new();
+    for k in 0..j.rows {
+        let Some(&b) = owner.get(k) else { continue };
+        let v = row(k);
+        let norm = dot(&v, &v).sqrt();
+        let mut w = v.clone();
+        // Twice, for the orthogonality lost to rounding.
+        for _ in 0..2 {
+            for qi in &q {
+                let d = dot(qi, &w);
+                for (wk, qk) in w.iter_mut().zip(qi) {
+                    *wk -= d * qk;
+                }
+            }
+        }
+        let left = dot(&w, &w).sqrt();
+        if let Some(h) = has_rows.get_mut(b) {
+            *h = true;
+        }
+        if norm.is_finite() && left.is_finite() && norm > 0.0 && left > DEPENDENT * norm {
+            q.push(w.iter().map(|wk| wk / left).collect());
+            basis.push((v, b));
+            if let Some(a) = adds_rank.get_mut(b) {
+                *a = true;
+            }
+        } else if Some(b) == support {
+            target_rows.push(v);
+        }
+    }
+    let dependent: Vec<bool> = has_rows.iter().zip(&adds_rank).map(|(h, a)| *h && !*a).collect();
+    let mut by = Vec::new();
+    if let Some(t) = support
+        && dependent.get(t).copied().unwrap_or(false)
+        && !basis.is_empty()
+    {
+        // The combination of the independent rows that gives each of the target's rows: the
+        // least-squares solution of Bᵀ a = v, from (B Bᵀ) a = B v (B has full row rank).
+        let m = basis.len();
+        let mut g = Mat::zeros(m, m);
+        for (r, (br, _)) in basis.iter().enumerate() {
+            for (c, (bc, _)) in basis.iter().enumerate() {
+                g.set(r, c, dot(br, bc));
+            }
+        }
+        for v in &target_rows {
+            let rhs: Vec<f64> = basis.iter().map(|(b, _)| dot(b, v)).collect();
+            let Some(a) = lin_solve(g.clone(), rhs) else { continue };
+            let big = a.iter().fold(0.0_f64, |m, x| m.max(x.abs()));
+            for (ak, (_, b)) in a.iter().zip(&basis) {
+                if ak.abs() > 1e-6 * big && !by.contains(b) {
+                    by.push(*b);
+                }
+            }
+        }
+        by.sort_unstable();
+    }
+    (dependent, by)
+}
+
+/// How far the constraint at index `ci` is from holding where the sketch is now: its largest
+/// residual (mm, or radians for angles). Zero for a constraint that holds, so a constraint that
+/// removes no degree of freedom but holds is redundant, not conflicting. `None` for a driven
+/// dimension (it constrains nothing) or an unknown index.
+pub fn constraint_residual(sk: &Sketch, ci: usize) -> Option<f64> {
+    let c = sk.constraints.get(ci).filter(|c| !c.driven)?;
+    let fixed = Layout { pvar: vec![None; sk.points.len()], rvar: vec![None; sk.curves.len()], n: 0, points: 0 };
+    let on_curve = points_on_curves(sk);
+    let b = match super::touch_point(sk, &c.kind, &on_curve) {
+        Some(p) => Block::TangentAt(ci, &c.kind, p),
+        None => Block::User(ci, &c.kind),
+    };
+    let mut r = Vec::new();
+    block_residuals(&State { sk, lay: &fixed, x: &[] }, &b, &mut r);
+    Some(max_abs(&r))
+}
+
+/// The constraints (indices) that already determine what the constraint at index `ci` asks
+/// for, where the sketch is now: the ones whose equations its own are a combination of. Empty
+/// when it is not redundant (it removes a degree of freedom), or when its component is too
+/// large to check.
+pub fn determined_by(sk: &Sketch, ci: usize) -> Vec<usize> {
+    let lay = layout(sk, &Hold::default());
+    let mut x = initial_x(sk, &lay);
+    let on_curve = points_on_curves(sk);
+    let (blocks, _) = build_blocks(sk, &lay, &on_curve);
+    let Some(t) = blocks.iter().position(|(b, _)| block_constraint(b) == Some(ci)) else { return Vec::new() };
+    let mut parent: Vec<usize> = (0..lay.n).collect();
+    for (_, vars) in &blocks {
+        if let Some(&first) = vars.first() {
+            for &v in vars.iter().skip(1) {
+                union(&mut parent, first, v);
+            }
+        }
+    }
+    let Some(root) = blocks.get(t).and_then(|(_, v)| v.first().copied()).map(|v| find(&mut parent, v)) else { return Vec::new() };
+    let vars: Vec<usize> = (0..lay.n).filter(|v| find(&mut parent, *v) == root).collect();
+    if vars.len() > MAX_REDUNDANCY_VARS {
+        return Vec::new();
+    }
+    // The component's other blocks in order, then the constraint asked about.
+    let mut order: Vec<usize> = (0..blocks.len())
+        .filter(|bi| *bi != t && blocks.get(*bi).and_then(|(_, v)| v.first()).is_some_and(|v| find(&mut parent, *v) == root))
+        .collect();
+    order.push(t);
+    let sub: Vec<(Block, Vec<usize>)> = order.iter().filter_map(|bi| blocks.get(*bi).map(|(b, v)| (super::copy_block(b), v.clone()))).collect();
+    let (_, by) = dependent_blocks(sk, &lay, &sub, &vars, &mut x, Some(sub.len().saturating_sub(1)));
+    let mut out: Vec<usize> = by.iter().filter_map(|k| sub.get(*k).and_then(|(b, _)| block_constraint(b))).collect();
+    out.sort_unstable();
+    out.dedup();
+    out
+}
@@ -21,6 +21,10 @@ use crate::linalg::{Mat, determined_vars, solve as lin_solve};
 use crate::model::{ConstraintKind, CurveKind, Sketch};
 use crate::union_find::{find, union};

+#[path = "redundancy.rs"]
+mod redundancy;
+pub use redundancy::{CONSISTENT, constraint_residual, determined_by};
+
 const MAX_ITERS: usize = 500;
 /// Variables in one connected component. Each component is solved as a dense system: an n by n
 /// matrix for the Levenberg-Marquardt step, rows by n for the Jacobian. 4,000 variables is a
@@ -65,6 +69,12 @@ pub struct SolveReport {
    pub point_determined: Vec<bool>,
    /// Per curve: all of its defining values determined.
    pub curve_determined: Vec<bool>,
+    /// Constraints that remove no degree of freedom: everything they ask for is already implied
+    /// by the constraints before them (a second "vertical" on a side two rectangles share).
+    /// They hold, so they are not a conflict; they are shown as redundant. Only from a full
+    /// analysis, and only for components of at most a few hundred variables.
+    #[serde(default)]
+    pub redundant: Vec<String>,
 }

 impl SolveReport {
@@ -1298,6 +1308,60 @@ impl Sketch {
    }
 }

+/// The variables' values where the sketch is now.
+fn initial_x(sk: &Sketch, lay: &Layout) -> Vec<f64> {
+    let mut x = vec![0.0; lay.n];
+    for (i, p) in sk.points.iter().enumerate() {
+        if let Some(v) = lay.pvar.get(i).copied().flatten() {
+            set_point(&mut x, v, p.pos);
+        }
+    }
+    for (i, c) in sk.curves.iter().enumerate() {
+        if let (CurveKind::Circle { r, .. } | CurveKind::Ellipse { r, .. }, Some(v)) = (&c.kind, lay.rvar.get(i).copied().flatten())
+            && let Some(s) = x.get_mut(v)
+        {
+            *s = *r;
+        }
+    }
+    x
+}
+
+/// The solve's blocks in order (the curves' own relations, then the driving constraints in
+/// constraint order) with the variables each reads, and per block whether it reads a constant
+/// point.
+fn build_blocks<'a>(sk: &'a Sketch, lay: &Layout, on_curve: &[(usize, usize)]) -> (Vec<(Block<'a>, Vec<usize>)>, Vec<bool>) {
+    let mut raw = Vec::new();
+    for c in &sk.curves {
+        if let CurveKind::Spline { pts, periodic: true, .. } = &c.kind
+            && let (Some(a), Some(b)) = (pts.first(), pts.last())
+            && a != b
+        {
+            raw.push(Block::Closure { a: *a, b: *b });
+        }
+        if let CurveKind::Arc { c, a, b } = c.kind {
+            raw.push(Block::Arc { c, a, b });
+        }
+    }
+    for (i, c) in sk.constraints.iter().enumerate() {
+        if c.driven {
+            continue;
+        }
+        raw.push(match touch_point(sk, &c.kind, on_curve) {
+            Some(p) => Block::TangentAt(i, &c.kind, p),
+            None => Block::User(i, &c.kind),
+        });
+    }
+    let mut blocks: Vec<(Block, Vec<usize>)> = Vec::with_capacity(raw.len());
+    let mut reads_constant = Vec::with_capacity(raw.len());
+    for bl in raw {
+        let (vars, constant) = block_vars(sk, lay, &bl);
+        blocks.push((bl, vars));
+        reads_constant.push(constant);
+    }
+
+    (blocks, reads_constant)
+}
+
 #[cfg(not(test))]
 fn solve_from(
    sk: &mut Sketch,
@@ -1721,19 +1785,7 @@ fn solve_inner(
        }
    }
    let lay = layout(sk, hold);
-    let mut x = vec![0.0; lay.n];
-    for (i, p) in sk.points.iter().enumerate() {
-        if let Some(v) = lay.pvar.get(i).copied().flatten() {
-            set_point(&mut x, v, p.pos);
-        }
-    }
-    for (i, c) in sk.curves.iter().enumerate() {
-        if let (CurveKind::Circle { r, .. } | CurveKind::Ellipse { r, .. }, Some(v)) = (&c.kind, lay.rvar.get(i).copied().flatten())
-            && let Some(s) = x.get_mut(v)
-        {
-            *s = *r;
-        }
-    }
+    let mut x = initial_x(sk, &lay);
    let x0 = x.clone();
    let on_curve = points_on_curves(sk);
    // Start from the constructed positions of the points the constraints pin down (see
@@ -1785,34 +1837,7 @@ fn solve_inner(
    nudge_line_angles(sk, &lay, &mut x);

    // The blocks, and per block whether it reads a constant point.
-    let mut raw = Vec::new();
-    for c in &sk.curves {
-        if let CurveKind::Spline { pts, periodic: true, .. } = &c.kind
-            && let (Some(a), Some(b)) = (pts.first(), pts.last())
-            && a != b
-        {
-            raw.push(Block::Closure { a: *a, b: *b });
-        }
-        if let CurveKind::Arc { c, a, b } = c.kind {
-            raw.push(Block::Arc { c, a, b });
-        }
-    }
-    for (i, c) in sk.constraints.iter().enumerate() {
-        if c.driven {
-            continue;
-        }
-        raw.push(match touch_point(sk, &c.kind, &on_curve) {
-            Some(p) => Block::TangentAt(i, &c.kind, p),
-            None => Block::User(i, &c.kind),
-        });
-    }
-    let mut blocks: Vec<(Block, Vec<usize>)> = Vec::with_capacity(raw.len());
-    let mut reads_constant = Vec::with_capacity(raw.len());
-    for bl in raw {
-        let (vars, constant) = block_vars(sk, &lay, &bl);
-        blocks.push((bl, vars));
-        reads_constant.push(constant);
-    }
+    let (blocks, reads_constant) = build_blocks(sk, &lay, &on_curve);

    carry_with_seeded(&mut x, &x0, &constructed, &blocks, &lay);
    // The plain start, for the variables whose start the seed (or carrying along it) moved.
@@ -1981,6 +2006,7 @@ fn solve_inner(
    let mut failing: Vec<String> = Vec::new();
    let mut det = vec![false; lay.n];
    let mut rank = 0;
+    let mut redundant: Vec<String> = Vec::new();
    // A component too large to solve is a failure, not an allocation.
    if comps.iter().any(|(_, vars, bis)| !bis.is_empty() && oversized(vars)) {
        max_residual = f64::MAX;
@@ -2023,6 +2049,17 @@ fn solve_inner(
        let (rest_det, rest_rank) = if j.rows > 0 { determined_vars(&j, 1e-7) } else { (vec![false; rest.len()], 0) };
        let comp_rank = pin_flags.iter().filter(|p| **p).count() + rest_rank;
        rank += comp_rank;
+        // More rows than rank: some constraint may be implied by the others.
+        if r.len() > comp_rank && vars.len() <= redundancy::MAX_REDUNDANCY_VARS {
+            let (dependent, _) = redundancy::dependent_blocks(sk, &lay, &sub, vars, &mut x, None);
+            for ((b, _), d) in sub.iter().zip(dependent) {
+                if d && let Some(c) = redundancy::block_constraint(b).and_then(|ci| sk.constraints.get(ci))
+                    && !redundant.contains(&c.id)
+                {
+                    redundant.push(c.id.clone());
+                }
+            }
+        }
        for (&v, pinned) in vars.iter().zip(&pin_flags) {
            let flag = match rest.binary_search(&v) {
                Ok(k) => rest_det.get(k).copied().unwrap_or(false),
@@ -2171,6 +2208,7 @@ fn solve_inner(
        continuations,
        point_determined,
        curve_determined,
+        redundant,
    }
 }

@@ -128,7 +128,7 @@ pub fn begin_dimension(app: &mut SolveApp, entities: Vec<String>, at: Vec2) -> R
    if draft.driven {
        PLACEMENT.with(|preview| *preview.borrow_mut() = None);
        app.run("sketch.dimension", json!({"entities": draft.entities, "text_at": [at.x, at.y], "driven": true}))?;
-        app.set_status("That dimension would over-constrain the sketch, so it was added as a driven (reference) dimension", false);
+        app.set_status("The sketch already determines that dimension, so it was added as a driven (reference) dimension", false);
        return Ok(());
    }
    EDIT.with(|edit| *edit.borrow_mut() = Some(Edit { param, expr, at: None, fresh: FRESH, wait: 10, draft: Some(draft), live: None }));
@@ -156,13 +156,15 @@ pub fn lines(sk: &Sketch, prev: Vec2, lp: Vec2, tol: f64) -> Option<Inference> {
 pub fn commit(app: &mut SolveApp, line: &str, end: Vec2) {
    let Some(i) = current().filter(|i| i.at.dist(end) < 1e-9) else { return };
    clear();
-    let (cmd, params) = match i.kind {
+    let (cmd, mut params) = match i.kind {
        Kind::Parallel => ("sketch.constraint.parallel", json!({"a": i.curve, "b": line})),
        Kind::Perpendicular => ("sketch.constraint.perpendicular", json!({"a": i.curve, "b": line})),
        Kind::Tangent => ("sketch.constraint.tangent", json!({"a": i.curve, "b": line})),
        Kind::Extension => ("sketch.constraint.coincident", json!({"a": format!("{line}.end"), "b": i.curve})),
    };
-    // An inference that would over-constrain the sketch is simply not kept.
+    // An inference only adds what the sketch does not already have: one that is already implied
+    // (redundant) or would conflict is simply not kept.
+    params["if_redundant"] = json!("refuse");
    let _ = app.session.execute(cmd, &params);
 }

@@ -0,0 +1,73 @@
+//! Rectangles of one size drawn by clicking around a shared corner (a "clover"): each one's
+//! corner snaps onto the corners already there and its typed width and height go in. None is
+//! refused as over-constraining the sketch (#687).
+
+use serde_json::json;
+
+use crate::scenario::Harness;
+
+fn type_value(h: &mut Harness, text: &str) {
+    h.step(&json!({"key": "A", "cmd": true})).unwrap();
+    h.step(&json!({"text": text})).unwrap();
+}
+
+/// Draw a rectangle from `a` (clicked, snapping onto what is there) towards `b`, typing its
+/// width and height when given, else clicking `b`.
+fn rectangle(h: &mut Harness, a: [f64; 2], b: [f64; 2], typed: bool) {
+    h.step(&json!({"start": "sketch.rectangle.two_point"})).unwrap();
+    h.step(&json!({"click": {"world": [a[0], a[1], 0]}})).unwrap();
+    h.step(&json!({"move": {"world": [b[0], b[1], 0]}})).unwrap();
+    if typed {
+        type_value(h, "10");
+        h.step(&json!({"key": "Tab"})).unwrap();
+        type_value(h, "10");
+        h.step(&json!({"key": "Enter"})).unwrap();
+    } else {
+        h.step(&json!({"click": {"world": [b[0], b[1], 0]}})).unwrap();
+    }
+    h.step(&json!({"key": "Escape"})).unwrap();
+    h.settle();
+}
+
+const CLOVER: [([f64; 2], [f64; 2]); 4] = [([0., 0.], [-10., -10.]), ([0., 0.], [10., -10.]), ([0., 0.], [10., 10.]), ([0., 0.], [-10., 10.])];
+
+#[test]
+fn a_clover_of_typed_10_by_10_rectangles_is_drawn_and_fully_constrained() {
+    let mut h = Harness::new();
+    h.app.run("sketch.create", json!({"plane": "XY"})).unwrap();
+    for (i, (a, b)) in CLOVER.iter().enumerate() {
+        rectangle(&mut h, *a, *b, true);
+        if let Some((message, _, true)) = &h.app.status {
+            panic!("rectangle {i} was refused: {message}");
+        }
+        let state = h.app.session.world_state();
+        let solved = state.sketch(h.app.session.active_sketch.unwrap()).unwrap();
+        assert_eq!(solved.sketch.curves.iter().filter(|c| !c.construction).count(), 4 * (i + 1), "rectangle {i} was not added");
+        assert!(solved.report.ok());
+    }
+    let state = h.app.session.world_state();
+    let solved = state.sketch(h.app.session.active_sketch.unwrap()).unwrap();
+    assert_eq!(solved.profiles.len(), 4);
+    assert!(solved.profiles.iter().all(|p| (p.area - 100.0).abs() < 1e-6), "{:?}", solved.profiles.iter().map(|p| p.area).collect::<Vec<_>>());
+    assert!(solved.report.fully_constrained(), "the clover on the origin, every size typed: {:?}", solved.report);
+}
+
+#[test]
+fn a_clover_drawn_by_clicks_snaps_every_corner_without_redundant_constraints() {
+    let mut h = Harness::new();
+    h.app.run("sketch.create", json!({"plane": "XY"})).unwrap();
+    // Clicked, the last one goes from corner to corner of the ones already there, so both its
+    // clicks snap (a free click lands only as near as the pointer allows).
+    let mut clover = CLOVER;
+    clover[3] = ([0., 10.], [-10., 0.]);
+    for (a, b) in clover {
+        rectangle(&mut h, a, b, false);
+    }
+    assert!(h.app.status.as_ref().is_none_or(|(_, _, error)| !error), "{:?}", h.app.status);
+    let state = h.app.session.world_state();
+    let solved = state.sketch(h.app.session.active_sketch.unwrap()).unwrap();
+    assert_eq!(solved.profiles.len(), 4);
+    assert!(solved.report.ok() && solved.report.redundant.is_empty(), "{:?}", solved.report);
+    // On the origin: the two column widths and the two row heights are left.
+    assert_eq!(solved.report.dof, 4);
+}
@@ -377,3 +377,7 @@ mod tests;
 #[cfg(test)]
 #[path = "sketch_typed_intent_tests.rs"]
 mod typed_intent_tests;
+
+#[cfg(test)]
+#[path = "sketch_clover_ui_tests.rs"]
+mod clover_ui_tests;
@@ -1086,6 +1086,8 @@ fn glyphs(app: &SolveApp, painter: &egui::Painter, proj: &Proj, hover: Option<Po
    for (id, sp, base) in &placed {
        let Some(c) = ss.sketch.constraints.iter().find(|c| &c.id == id) else { continue };
        let failing = ss.report.failing.contains(id);
+        // Redundant (already implied by the others, but holding): dimmed, not an error.
+        let redundant = !failing && ss.report.redundant.contains(id);
        let selected = picked.as_deref() == Some(id.as_str())
            || app.session.selection.iter().any(|s| matches!(s, solidcraft_engine::Sel::SketchConstraint { id: x } if x == id));
        let lit = selected || hovered.as_deref() == Some(id.as_str());
@@ -1093,6 +1095,8 @@ fn glyphs(app: &SolveApp, painter: &egui::Painter, proj: &Proj, hover: Option<Po
            tk.error
        } else if lit {
            tk.accent
+        } else if redundant {
+            tk.glyph_text.gamma_multiply(0.45)
        } else {
            tk.glyph_text
        };
@@ -1114,7 +1118,11 @@ fn glyphs(app: &SolveApp, painter: &egui::Painter, proj: &Proj, hover: Option<Po
    if let (Some(id), Some(h)) = (hovered, hover)
        && let Some(c) = ss.sketch.constraints.iter().find(|c| c.id == id)
    {
-        let label = format!("{} ({id})", c.kind.name());
+        let label = if ss.report.redundant.contains(&id) {
+            format!("{} ({id}), redundant: already implied by other constraints", c.kind.name())
+        } else {
+            format!("{} ({id})", c.kind.name())
+        };
        let at = h + egui::vec2(12.0, 12.0);
        let g = painter.layout_no_wrap(label, egui::FontId::proportional(11.0), tk.text);
        painter.rect_filled(egui::Rect::from_min_size(at, g.size()).expand(3.0), 3.0, tk.panel);