Query:
?- reachable(a).
Answer:
Model:
{ reachable(a), in(d,a), reachable(d), in(b,d), reachable(b), in(a,b) }
Justification:
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reachable(a) :-
in(d,a) :-
edge(d,a),
proved(edge(d,a)).
reachable(d) :-
in(b,d) :-
edge(b,d),
proved(edge(b,d)).
reachable(b) :-
in(a,b) :-
edge(a,b),
proved(edge(a,b)).
global_constraint :-
not o_chk_1 :-
proved(in(a,b)),
edge(a,c),
ex(a,c) :-
proved(edge(a,c)).
edge(b,c),
ex(b,c) :-
proved(edge(b,c)).
proved(in(b,d)),
edge(c,d),
ex(c,d) :-
proved(edge(c,d)).
proved(in(d,a)).
not o_chk_2 :-
proved(in(a,b)),
proved(in(b,d)),
proved(in(d,a)).