'If \'self\' is bound by \'bindings\', return the atomic to which it is bound.
Otherwise, return self.
:param bindings: ``BindingDict`` A dictionary of bindings used to simplify
:return: ``AtomicExpression``'

def simplify(self, bindings=None):

    if (bindings and (self in bindings)):
        return bindings[self]
    else:
        return self
