2 | 9. L:Vertices(the_graph) List, s:traversal(the_graph).
s2:traversal(the_graph). list_accum(s',j.dfs(the_obj;s';j);s;L) = (s2 @ s) s':traversal(the_graph). ((inr(i) s) (inl(i) s)  s' = nil) & ( (inr(i) s) & (inl(i) s)  ( s2:traversal(the_graph). s' = ([inl(i)] @ s2 @ [inr(i)]) traversal(the_graph))) & [inl(i) / (the_obj.eacc(( s',j. dfs(the_obj;s';j)),[inr(i) / s],i))] = (s' @ s) traversal(the_graph) | 4 steps |