is mentioned by

Def topsortedl(the_graph;L;s) == (i,j:Vertices(the_graph). j = i i-the_graph- > *j i before j s) & (i,j,k:Vertices(the_graph). k-the_graph- > *j k-the_graph- > *i (k':Vertices(the_graph). k' before k L k'-the_graph- > *i) i before j s)	[topsortedl]
Def topsorted(the_graph;s) == i,j:Vertices(the_graph). i-the_graph- > *j i = j i before j s	[topsorted]

In prior sections: mb list 1 mb list 2 graph 1 1

Try larger context: Graphs