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Fixes #4391.
The sets cardinality cycle rule is analogous to the S-Cycle rule for strings (see Liang et al CAV 2014). This rule is typically never applied but can be applied in rare cases where theory combination does not determine a correct arrangement of equalities over sets terms that is consistent with the arithmetic arrangement of their cardinalities at full effort. Notice the regression from #4391 has non-linear arithmetic, (mod 0 d), which is translated to UF.
The cardinality cycle rule had a bug: it assumed that cycles that were encountered were loops e1 = e2 = ... = e1 but in general they can be lassos e1 = ... = e2 = ... = e2. This ensures the Venn region cycle e2 = ... = e2 is the conclusion in this case, instead of unsoundly concluding e1 = ... = e2.
Strings does not have a similar issue:
https://github.com/CVC4/CVC4/blob/master/src/theory/strings/core_solver.cpp#L488
Here, when a cycle is encountered, it is processed at the point in traversal where the loop is closed.
This is not critical for SMT-COMP but should be in the 1.8 release.
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