| 1 | 25. L1@0 = L1 26. [i] = L2 27. i:Vertices(the_graph). (inl(i) s)  L1-the_graph- > *i 28. e = nil s1,s2@0:traversal(the_graph). (([inl(i)] @ s2 @ [inr(i)]) @ s) = (s2@0 @ s1) traversal(the_graph) & paren(Vertices(the_graph);s1) & paren(Vertices(the_graph);s2@0) & ( j:Vertices(the_graph). ((inl(j) s1)  L1-the_graph- > *j) & ((inl(j) s2@0)  [i]-the_graph- > *j & L1-the_graph- > *j)) | 27 steps |