Hotfix: canonicalizeSpotTrace corrupts traces with OR operators#149
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Hotfix: canonicalizeSpotTrace corrupts traces with OR operators#149
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Bug
Trace satisfaction Y/N questions were showing the wrong correct answer for formulas like s <-> v. A question with trace !s & v; cycle{s & !v} against formula (s <-> v) was displaying Yes as the correct answer when it should have been No.
Root Cause
Introduced in v1.9.10 (commit 4cc9cd4, PR #146).
canonicalizeSpotTrace calls _canonicalize_state directly on raw SPOT trace output. However, _canonicalize_state only understands &-separated literals — it has no awareness of | (OR) operators.
SPOT generates trace states that can contain ORs, e.g.:
The canonicalizer was:
Splitting on & → tokens like (s, v) | (!s, !v)
Stripping parentheses → s, v | !s, !v (garbled)
Reordering alphabetically → s & !v & v | !s (nonsensical)
This destroyed the OR structure, producing traces that no longer satisfied (or rejected) the original formula. Since the correctness label (Yes/No) was determined before canonicalization, but the displayed trace was the corrupted one, students saw wrong answers.
Fix
Added _resolve_ors_in_state() which calls choosePathFromWord (the existing OR-resolver via the LTL parser) on each trace state before canonicalizing. This is the same OR-resolution that NodeRepr.init already performs — canonicalizeSpotTrace was simply bypassing it.
Verification
Ran a 100-iteration simulation of question generation for s <-> v: 0 bugs (previously ~40% failure rate)
3 new regression tests added for OR-containing traces
Full test suite passes (4 pre-existing English translation failures unrelated to this change)
Changes
exerciseprocessor.py — added _resolve_ors_in_state, integrated into canonicalizeSpotTrace
test_trace_canonicalization.py — 3 new regression tests
version.html — bumped to 1.9.12
CHANGELOG.md — added bugfix entry