<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def add_child_hash(self, child_hash):
 """ Adds specified child hash. The hash must be one of the binary types. """


        # Hash must generate binary keys
        if not (isinstance(child_hash,PCABinaryProjections) or isinstance(child_hash,RandomBinaryProjections) or isinstance(child_hash,RandomBinaryProjectionTree)):
            raise ValueError('Child hashes must generate binary keys')

        # Add both hash and config to array of child hashes. Also we are going to
        # accumulate used bucket keys for every hash in order to build the permuted index
        self.child_hashes.append(child_hash)