1. A method comprising: identifying a set of input vectors within an input space of a design; dividing the set of input vectors into multiple subsets of the input vectors; determining, using a first satisfiability solver, that at least one of the subsets does not provide a solution to a set of input constraints; and searching, using a second satisfiability solver, the multiple subsets for unique input vectors that satisfy the set of input constraints, wherein the searching excludes a sub-searching of the at least one of the subsets.