#show in/2.

%in(X,Y) :- edge(X,Y), not out(X,Y).
%out(X,Y) :- edge(X,Y), not in(X,Y).
{in(X,Y)} :- edge(X,Y).
:- in(X,Y), in(X,Z), Y!=Z.
:- in(X,Z), in(Y,Z), X!=Y.

reached(X) :- in(1,X).
reached(Y) :- reached(X), in(X,Y).

:- vtx(X), not reached(X).