def _find_unchanged(old, new):
edges = []<EOL>old_edges = [set(edge) for edge in old.edges()]<EOL>new_edges = [set(edge) for edge in new.edges()]<EOL>for old_edge in old_edges:<EOL><INDENT>if old_edge in new_edges:<EOL><INDENT>edges.append(set(old_edge))<EOL><DEDENT><DEDENT>return edges<EOL>
returns edges that are in both old and new