is mentioned by

Thm* For any graph the_obj:GraphObject(the_graph), L:V List. (i:V. (i L)) (non-trivial-loop-free(the_graph) topsortedl(the_graph;L;topsortl(the_obj;L))) & (i:V. (i topsortl(the_obj;L))) & no_repeats(V;topsortl(the_obj;L))

[topsortl-properties]

Try larger context: Graphs