4     for elt in tup:
5         if isinstance(elt, tuple):
6             elts = elts + flatten(elt)
8             elts.append(elt)
16     def __contains__(self, elt):  argument
17         return elt in self.elts
18     def add(self, elt):  argument
19         self.elts[elt] = elt
22     def has_elt(self, elt):  argument
23         return elt in self.elts
24     def remove(self, elt):  argument
25         del self.elts[elt]
37     def push(self, elt):  argument
38         self.stack.append(elt)