is mentioned by

Thm* For any graph the_obj:GraphObject(the_graph). (x,y:V. the_obj.eq(x,y) x = y) & (T:Type, s:T, x:V, f:(TVT). L:V List. (y:V. x-the_graph- > y (y L)) & the_obj.eacc(f,s,x) = list_accum(s',x'.f(s',x');s;L)) & (T:Type, s:T, f:(TVT). L:V List. no_repeats(V;L) & (y:V. (y L)) & the_obj.vacc(f,s) = list_accum(s',x'.f(s',x');s;L))	[graphobj-properties]
Thm* For any graph t:GraphObject(the_graph). t.vaccw (T:Type, s:T, f:(TVT). L:V List. no_repeats(V;L) & (y:V. (y L)) & t.vacc(f,s) = list_accum(s',x'.f(s',x');s;L))	[gro_vaccw_wf]
Def depthfirst(the_obj) == the_obj.vacc((s,i. dfs(the_obj;s;i)),nil)	[depthfirst]
Def vertex-subset(the_obj;x.P(x)) == the_obj.vacc((l,x. if P(x) [x / l] else l fi),nil)	[vertex-subset]

Try larger context: Graphs