Returns True whether `e` is a concrete value or is a value set with
        only 1 possible value. This differs from `unique` in that this *does*
        not query the constraint solver.

def single_valued(self, e):
        """
        Returns True whether `e` is a concrete value or is a value set with
        only 1 possible value. This differs from `unique` in that this *does*
        not query the constraint solver.
        """
        if self.state.mode == 'static':
            if type(e) in (int, bytes, float, bool):
                return True
            else:
                return e.cardinality <= 1

        else:
            # All symbolic expressions are not single-valued
            return not self.symbolic(e)