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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 is_causal_source(graph: BELGraph, node: BaseEntity) -> bool: """Return true of the node is a causal source. - Doesn't have any causal in edge(s) - Does have causal out edge(s) """

    # TODO reimplement to be faster
    return not has_causal_in_edges(graph, node) and has_causal_out_edges(graph, node)