def predicates(self):
        if isinstance(self.function, ConstantExpression):
            function_preds = set([self.function.variable])
        else:
            function_preds = self.function.predicates()
        return function_preds | self.argument.predicates()
:see: Expression.predicates()
dataset/ETHPy150Open nltk/nltk/nltk/sem/logic.py/ApplicationExpression.predicates