- New nseq_nielsen.h/cpp in src/ast/rewriter/: self-contained Nielsen
transformation engine for word equations
- simplify(): strip common prefix/suffix, empty elimination, variable
stripping, single-var assignment detection
- split(): case analysis for var vs constant, var vs var
- is_conflict(): mismatch detection (different constants, one side
has constants while other is empty)
- Wire Nielsen into theory_nseq:
- solve_eqs()/solve_eq(): process word equations using Nielsen
transformations with e-graph canonization
- branch_eq()/branch_var_prefix(): binary empty/non-empty decisions
and prefix enumeration (no fresh variable creation)
- canonize(): rewrite equation sides using current e-graph equivalences
- all_eqs_solved(): check if all equations are satisfied
- mk_value(): basic model generation (walk e-class for string constants)
- Passes basic tests: simple equalities, concat equations, unsat detection
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
