On Incremental Pre-processing for SMT

We introduce a calculus for incremental pre-processing for SMT and instantiate it in the context of z3. It identifies when powerful formula simplifications can be retained when adding new constraints. Use cases that could not be solved in incremental mode can now be solved incrementally thanks to the availability of pre-processing. Our approach admits a class of transformations that preserve satisfiability, but not equivalence. We establish a taxonomy of pre-processing techniques that distinguishes cases where new constraints are modified or constraints previously added have to be replayed. We then justify the soundness of the proposed incremental pre-processing calculus.