Add MaximumClique<SimpleGraph, One> variant with weight cast and reductions

[GiggleLiu]

Summary

• Register MaximumClique<SimpleGraph, One> variant so reduction paths from MIS<SimpleGraph, One> no longer require unnecessary weight promotion to i32 before reaching MaximumClique.
• Add maximumclique_casts.rs covering the new One variant and ensure round-tripping from MIS to MaxClique works without weight promotion.
• Consolidate three duplicate complement_edges implementations into graph_helpers::complement_edges (DRY).

Test plan

• `make test` passes
• `make clippy` reports no warnings
• `pred path MaximumIndependentSet MaximumClique` resolves without forcing an `i32` detour for unit-weight inputs

[GiggleLiu]

Agentic Review Report

Note: PR head (1e17e9df) was opened against ff8ae70e; origin/main has since advanced to 9ff62f0d (#1056). A rebase/merge of main will be needed before final merge.

Note: This PR is not tracked on the project board (no card in Review pool). Review was performed manually per explicit request; no board transitions were applied.

Structural Check

Rule Checklist

#	Check	Status
1	Rule file exists (src/rules/maximumclique_casts.rs)	PASS
2	#[reduction(...)] macro present (via impl_variant_reduction!)	PASS
3	ReductionResult impl (via ReductionAutoCast)	PASS
4	ReduceTo impl present	PASS
5	#[cfg(test)] mod tests #[path] link	FAIL — no link in file
6	Test file src/unit_tests/rules/maximumclique_casts.rs	FAIL — missing
7	Closed-loop test present	FAIL
8	Registered in src/rules/mod.rs	PASS (line 74)
9	Canonical rule example registered	N/A — weight-cast rules follow the same no-example convention as maximumindependentset_casts.rs
10	Paper reduction-rule entry	ACCEPTABLE — existing MIS↔MaxClique paper entries (docs/paper/reductions.typ lines 11103, 12694) cover both weight variants; cast edges are auto-filtered from the paper like existing MIS casts

Build / Test / Clippy

• cargo build --lib: PASS
• cargo clippy --lib --all-targets: PASS
• cargo test --lib: FAIL — 1 failing test:
  • rules::analysis::tests::test_find_dominated_rules_returns_known_set
• Directly-related tests (maximum_clique model tests, maximumclique_maximumindependentset, maximumindependentset_maximumclique, kcoloring_partitionintocliques): PASS.

Mathematical Correctness

• maximumclique_casts.rs (<SimpleGraph,One> → <SimpleGraph,i32>): identity graph, weights cast One → 1i32. Reduction is weight-preserving, extract_solution is identity, witness round-trip verified on a worked K3 example. OK.
• maximumclique_maximumindependentset.rs <One> branch (lines 67–73): takes the complement graph. On P5 (5 vertices, 4 edges), complement has 10 − 4 = 6 edges; identity extract maps clique config back to IS config. OK.
• graph_helpers::complement_edges (new consolidated helper at src/rules/graph_helpers.rs:62-73): emits (u,v) for u<v with !graph.has_edge(u,v). For P4 (edges (0,1),(1,2),(2,3)) produces (0,2),(0,3),(1,3) — 3 edges = C(4,2) − 3. Correct.

Overhead Verification

• maximumclique_casts.rs: identity overhead (num_vertices, num_edges). Preserves graph and vertex count. Exact.
• Complement-graph rules (MC↔MIS and KColoring→PartitionIntoCliques): num_edges = "num_vertices*(num_vertices - 1)/2 - num_edges". Matches C(n,2) − m. Correct.

Blocker — B1 (CI-breaking)

rules::analysis::tests::test_find_dominated_rules_returns_known_set rejects the newly-registered edge MaximumClique<SimpleGraph,One> → MaximumClique<SimpleGraph,i32> in src/rules/maximumclique_casts.rs:12-18:

Unexpected dominated rule:
  MaximumClique {graph: "SimpleGraph", weight: "One"}
    -> MaximumClique {graph: "SimpleGraph", weight: "i32"}
  dominated by:
  MC<SG,One> -> MIS<SG,One> -> MIS<SG,i32> -> MC<SG,i32>

The path MC<SG,One> → MIS<SG,One> → MIS<SG,i32> → MC<SG,i32> already existed on this branch and dominates the new direct cast edge.

Fix options (in order of preference):

• (a) Delete the cast edge in maximumclique_casts.rs (and consider deleting the now-empty file and its mod line). This preserves the stated PR goal — the <One> variant node, plus cast-free MIS paths — because the cast-less MC<SG,One>→MC<SG,i32> path is still reachable via MIS. Project convention per .claude/CLAUDE.md: "there is only one primitive reduction registration for each exact source/target variant pair."
• (b) Allow-list the edge in src/unit_tests/rules/analysis.rs with justification. Less aligned with project policy.

Other Structural Issues

• M1. Cast file has no #[cfg(test)] mod tests link. Consistent with existing maximumindependentset_casts.rs, but obsolete if B1 is fixed by deletion.
• M2. No direct <One>-endpoint closed-loop tests for the two reduction variants at maximumclique_maximumindependentset.rs:67-73 and maximumindependentset_maximumclique.rs:67-73; coverage is incidental through the existing <i32> suite exercising the shared helper.

Verdict: NEEDS CHANGES (blocker B1).

---

Quality Check

Design Principles

• DRY: PASS — three formerly-duplicated complement_edges call sites (kcoloring_partitionintocliques.rs, maximumclique_maximumindependentset.rs, maximumindependentset_maximumclique.rs) are all consolidated into a single helper graph_helpers::complement_edges (src/rules/graph_helpers.rs:62-73). Extracted reduce_clique_to_is/reduce_is_to_clique helpers factor out the body shared between i32 and One variants.
• KISS: PASS — maximumclique_casts.rs (18 lines) mirrors the pattern in maximumindependentset_casts.rs. No unnecessary abstraction.
• HC / LC: PASS — complement_edges lives in graph_helpers.rs alongside edges_to_cycle_order. Signature is clean.

Behavior Preservation of Refactor

All three prior complement_edges implementations were bit-identical: for u in 0..n { for v in (u+1)..n { if !graph.has_edge(u, v) { edges.push((u, v)); } } }. The unified helper copies this verbatim. Semantics preserved for all three call sites (kcoloring_partitionintocliques.rs:45, maximumclique_maximumindependentset.rs:39, maximumindependentset_maximumclique.rs:39).

HCI

• pred path MaximumIndependentSet MaximumClique now resolves to a single-step direct path on the <SimpleGraph, One> endpoint — no i32 detour. Confirmed empirically. Primary stated PR goal achieved.
• pred list shows MaximumClique/SimpleGraph/One as default (*) and MaximumClique/SimpleGraph/i32 as secondary, consistent with MaximumIndependentSet presentation.

Test Quality

• Existing closed-loop tests for both MC↔MIS directions continue to exercise the refactored helper path via the <SimpleGraph, i32> endpoint.
• Missing tests:
  • No closed-loop test for MaximumClique<SimpleGraph, One> → MaximumIndependentSet<SimpleGraph, One> (new reduction variant).
  • No closed-loop test for MaximumIndependentSet<SimpleGraph, One> → MaximumClique<SimpleGraph, One> (new reduction variant).
  • No test file for maximumclique_casts.rs (matches maximumindependentset_casts.rs precedent, but becomes moot if B1 is fixed by deletion).
• Model-side: src/unit_tests/models/graph/maximum_clique.rs is not updated to exercise One-weighted evaluation/solving.

Issues

• [important] Missing closed-loop tests for the two new <SimpleGraph, One> reduction endpoints (both directions). A 5-vertex path-graph test mirroring the existing i32 tests is sufficient.
• [important] Missing model-level test covering the new default MaximumClique<SimpleGraph, One> variant with One weights.
• [minor] reduce_clique_to_is / reduce_is_to_clique declare W: WeightElement + Clone + Default — Clone + Default are redundant since WeightElement: Clone + Default + 'static. Simplify to W: WeightElement. (maximumclique_maximumindependentset.rs:36, maximumindependentset_maximumclique.rs:36.)
• [minor] src/rules/kcoloring_partitionintocliques.rs:32 places the use super::graph_helpers::complement_edges; below the impl ReductionResult block rather than grouping with the other use statements at the top.
• [nit] Consider making complement_edges generic over G: Graph for consistency with edges_to_cycle_order; all current callers pass &SimpleGraph so no immediate functional gain.

---

Agentic Feature Tests

Run inline by review-pipeline after the dedicated subagent exited without a final report.

#	Command	Result
1	cargo build -p problemreductions-cli --bin pred	PASS
2	pred list | grep -i clique	PASS — MaximumClique/SimpleGraph/One * listed as default, MaximumClique/SimpleGraph/i32 shown as secondary
3	pred show MaximumClique	PASS — shows the new default variant; outgoing reductions → MaximumIndependentSet/SimpleGraph/One and → MaximumClique/SimpleGraph/i32; incoming MaximumIndependentSet/SimpleGraph/One →
4a	pred path MaximumIndependentSet MaximumClique	PASS — 1-step path MIS/SG/One → MaximumClique/SG/One; no i32 detour
4b	pred path MaximumClique MaximumIndependentSet	PASS — 1-step path MaximumClique/SG/One → MIS/SG/One; no i32 detour
5	pred create --example MaximumClique	FAIL — No canonical model example exists for MaximumClique/SimpleGraph/One. Pre-existing gap, not a regression: no MaximumClique example exists in src/example_db/model_builders.rs on main either (empty grep). Worth filing separately.
6	pred create MaximumClique --graph 0-1,1-2,2-3,3-4,4-0 --num-vertices 5 --weights 1,1,1,1,1	PASS — created instance, weight: "One" selected automatically
7	pred solve /tmp/mc5.json	PASS — solution [1,0,0,0,1] (max clique of size 2 on 5-cycle; correct — no triangles in C5)

Assessment. CLI-facing functionality works as advertised: the new <One> variant becomes the default for MaximumClique, and reduction paths between MIS and MaxClique now stay in unit-weight without the i32 promotion detour. One pre-existing gap (no canonical example for MaximumClique in example_db) surfaced during testing but is unrelated to this PR.

---

Combined Verdict

• Blocker: B1 — cargo test --lib fails on rules::analysis::tests::test_find_dominated_rules_returns_known_set because the new cast edge MaximumClique<SG,One> → MaximumClique<SG,i32> is dominated by the existing MC→MIS→MIS→MC path. Preferred fix: delete the cast edge (and likely the now-empty maximumclique_casts.rs). The <One> variant plus cast-free MIS paths are preserved.
• Important: Add closed-loop tests for the two new <SimpleGraph, One> MC↔MIS reduction endpoints and a model-level test for MaximumClique<SG,One>.
• Minor / nit: redundant trait bounds, use placement, possible generalization of complement_edges, pre-existing lack of canonical MaximumClique example.
• Good: DRY consolidation of complement_edges is clean and behavior-preserving; HCI goal (no i32 detour for MIS↔MaxClique on unit weights) is confirmed.

Generated by review-pipeline (run manually — PR is not on the project board).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.92%. Comparing base (9ff62f0) to head (59982df).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1055   +/-   ##
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  Coverage   97.92%   97.92%           
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  Files         966      966           
  Lines       99972   100043   +71     
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+ Hits        97896    97967   +71     
  Misses       2076     2076           

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