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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def fold(self, predicate):
 """Takes a predicate and applies it to each node starting from the leaves and making the return value propagate."""

        childs = {x:y.fold(predicate) for (x,y) in self._attributes.items()
                  if isinstance(y, SerializableTypedAttributesHolder)}
        return predicate(self, childs)