code: def is_true(self, e, extra_constraints=(), solver=None, model_callback=None): #pylint:disable=unused-argument
          
  
          #if self._solver_required and solver is None:
          #   raise BackendError("%s requires a solver for evaluation" % self.__class__.__name__)
          if not isinstance(e, Base):
              return self._is_true(self.convert(e), extra_constraints=extra_constraints, solver=solver, model_callback=model_callback)
  
          try:
              return self._true_cache[e.cache_key]
          except KeyError:
              t = self._is_true(self.convert(e), extra_constraints=extra_constraints, solver=solver, model_callback=model_callback)
              self._true_cache[e.cache_key] = t
              if t is True:
                  self._false_cache[e.cache_key] = False
              return t
docs: Should return True if `e` can be easily found to be True.
  
          :param e:                   The AST.
          :param extra_constraints:   Extra constraints (as ASTs) to add to the solver for this solve.
          :param solver:              A solver, for backends that require it.
          :param model_callback:      a function that will be executed with recovered models (if any)
          :returns:                   A boolean.