is mentioned by

Thm* G:Graph. (x,y:Vertices(G). Dec(x = y)) (s:traversal(G). paren(Vertices(G);s) no_repeats(Vertices(G)+Vertices(G);s) df-traversal(G;s) depthfirst-traversal(G;s))	[paren-df-traversal]
Thm* s:(T+T) List. paren(T;s) no_repeats(T+T;s) (s1,s2,s3:(T+T) List, x:T. s = (s1 @ [inl(x)] @ s2 @ [inr(x)] @ s3) paren(T;s2))	[paren_interval]

In prior sections: mb list 2 graph 1 1

Try larger context: Graphs