2 | 9. non-trivial-loop-free(the_graph) 10. L1,L2:Vertices(the_graph) List.
L = (L1 @ L2)

( s1,s2:Vertices(the_graph) List.
topsortl(the_obj;L) = (s2 @ s1)
& ( j:Vertices(the_graph).
((j s1)  L1-the_graph- > *j) & ((j s2)  L2-the_graph- > *j & L1-the_graph- > *j))) topsortedl(the_graph;L;topsortl(the_obj;L)) | 41 steps |