164       const NodeSet &Set;  variable
169         Current = Set.V.find_next(Current);  in advance()
173       iterator(const NodeSet &Set, size_type Begin)  in iterator()  argument
174           : Set{Set}, Current{Begin} {}  in iterator()
186         return Set.G.nodes_begin() + Current;
189         assert(&this->Set == &other.Set);
252       const EdgeSet &Set;  variable
257         Current = Set.V.find_next(Current);  in advance()
261       iterator(const EdgeSet &Set, size_type Begin)  in iterator()  argument
262           : Set{Set}, Current{Begin} {}  in iterator()
274         return Set.G.edges_begin() + Current;
277         assert(&this->Set == &other.Set);