complement-graph.vlog

% Complement of the transitive closure

v(X)    :- r(X,Y).
v(Y)    :- r(X,Y).
t(X,Y)  :- r(X,Y).
t(X,Y)  :- t(X,Z), r(Z,Y).
tc(X,Y) :- v(X), v(Y), ! t(X,Y).