is mentioned by

Def dfsl-traversal(the_graph;L;s) == df-traversal(the_graph;s) & (i:Vertices(the_graph). (inl(i) s) L-the_graph- > *i) & ((i:Vertices(the_graph). L-the_graph- > *i non-trivial-loop(the_graph;i)) (L1,L2:Vertices(the_graph) List. L = (L1 @ L2) (s1,s2:traversal(the_graph). s = (s2 @ s1) traversal(the_graph) & paren(Vertices(the_graph);s1) & paren(Vertices(the_graph);s2) & (j:Vertices(the_graph). ((inl(j) s1) L1-the_graph- > *j) & ((inl(j) s2) L2-the_graph- > *j & L1-the_graph- > *j)))))	[dfsl-traversal]
Def dfl-traversal(the_graph;L;s) == (i:Vertices(the_graph), s1,s2:traversal(the_graph). s = (s1 @ [inr(i)] @ s2) traversal(the_graph) (j:Vertices(the_graph). (inr(j) s2) (inl(j) s2) j-the_graph- > *i)) & (j:Vertices(the_graph). (inr(j) s) L-the_graph- > *j) & (i:Vertices(the_graph), s1,s2:traversal(the_graph). (j:Vertices(the_graph). i-the_graph- > *j non-trivial-loop(the_graph;j)) s = (s1 @ [inl(i)] @ s2) traversal(the_graph) L-the_graph- > *i)	[dfl-traversal]
Def depthfirst-traversal(the_graph;s) == i:Vertices(the_graph), s1,s2:traversal(the_graph). (j:Vertices(the_graph). i-the_graph- > *j non-trivial-loop(the_graph;j)) s = (s1 @ [inl(i)] @ s2) traversal(the_graph) (j:Vertices(the_graph). j = i i-the_graph- > *j (inl(j) s2))	[depthfirst-traversal]
Def df-traversal(G;s) == (i:Vertices(G), s1,s2:traversal(G). s = (s1 @ [inr(i)] @ s2) traversal(G) (j:Vertices(G). (inr(j) s2) (inl(j) s2) j-G- > *i)) & (i:Vertices(G), s1,s2:traversal(G). (j:Vertices(G). i-G- > *j non-trivial-loop(G;j)) s = (s1 @ [inl(i)] @ s2) traversal(G) (j:Vertices(G). i-G- > *j (inr(j) s2)))	[df-traversal]
Def non-trivial-loop-free(G) == i:Vertices(G). non-trivial-loop(G;i)	[non-trivial-loop-free]

Try larger context: Graphs