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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 encode_branch_node(left_child_node_hash, right_child_node_hash):
 """ Serializes a branch node """

    validate_is_bytes(left_child_node_hash)
    validate_length(left_child_node_hash, 32)
    validate_is_bytes(right_child_node_hash)
    validate_length(right_child_node_hash, 32)
    return BRANCH_TYPE_PREFIX + left_child_node_hash + right_child_node_hash