def get_peripheral_successor_edges(graph: BELGraph, subgraph: BELGraph) -> EdgeIterator:
for u in subgraph:<EOL><INDENT>for _, v, k in graph.out_edges(u, keys=True):<EOL><INDENT>if v not in subgraph:<EOL><INDENT>yield u, v, k<EOL><DEDENT><DEDENT><DEDENT>
Get the set of possible successor edges peripheral to the sub-graph.

    The source nodes in this iterable are all inside the sub-graph, while the targets are outside.