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An undecided member of an intersection stays in it - #1681
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Rafael-SOWNet merged 1 commit intoOct 2, 2026
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A member of a listed set whose membership in the other set could not be decided was kept in their
intersection unconditionally, so { y } /\ { 2 } was { y }, wrong at every y but 2, and Solve,
which meets the solution sets of a conjunction's sides, dropped an equation with a parameter in
it: x = y and x = 2 solved to { y }. Such a member now stays intersected with the other set,
beside the members that are decided.
Closes #1680.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012sonx8iAspMiwRwokT1Ura
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Closes #1680.
A member of a listed set whose membership in the other set can't be decided was kept in their intersection unconditionally. So
{ y } /\ { 2 }was{ y }, which is wrong at everyybut 2.Solvemeets the solution sets of a conjunction's two sides, so the same thing dropped an equation with a parameter in it. Now such a member stays intersected with the other set, beside the members that are decided:{ y } /\ { 2 }{ y }{ y } /\ { 2 }{ y, 3 } /\ { 3 }{ y } \/ { 3 }{ 3 } \/ { y } /\ { 3 }"x = y and x = 2".Solve("x"){ y }, which reads{ 1 }aty = 1{ y } /\ { 2 }, empty aty = 1"x + y = 3 and x - y = 1".Solve("x"){ 3 - y }{ 3 - y } /\ { 1 + y }:{ 2 }aty = 1, empty elsewhere"x^2 = 4 and x = y".Solve("x"){ 2, -2 }{ 2, -2 } /\ { y }A conjunction whose members are all decided is unchanged:
x = 2 and x = 3is{ },x^2 = 4 and not x = 2is{ -2 }.Tests:
ConjunctionFilterTest.ListedSetsWithAParameterMeetWhereTheyAgree(six rows, each with the parameter pinned on both sides of where the sets meet) andAnUndecidedMemberOfAnIntersectionStaysInIt(four).SolveEquationWithConstraints.TestFiniteIntersection, skipped as "Sets require more work", runs now and asserts the right answer:x^2 = a and x = ais{ 0 }ata = 0,{ 1 }ata = 1, and empty elsewhere.The suite passes, 14,334 tests. CasBench (120/121, 0 wrong), BoundCheck (0 disagreements), CanonCheck and Confluence (findings unchanged) pass, and so does the allocation gate.
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