@Override
 public Result solve(Expression<Boolean> exprsn, Valuation vltn) {
   if (!filter.submitToSolver(exprsn)) {
     return Result.DONT_KNOW;
   }
   return solver.solve(exprsn, vltn);
 }
 @Override
 public SimpleSelectiveSolverContext createContext() {
   SolverContext ctx = solver.createContext();
   return new SimpleSelectiveSolverContext(ctx, filter, evaluate);
 }