#hide.
#show black/2.
col(0..n-1).
row(0..n-1).

#domain row(X).
#domain col(Y).
#domain number(N).

0 {black(X,Y)} 1.

:- black(X,Y), black(X+1,Y), row(X+1).
:- black(X,Y), black(X,Y+1), col(Y+1).

:- cell(X,Y,N), cell(X,Z,N), Y<Z, not black(X,Y), not black(X,Z), col(Z).
:- cell(X,Y,N), cell(Z,Y,N), X<Z, not black(X,Y), not black(Z,Y), row(Z).

adjacent(X,Y,X,Y-1):-col(Y-1).
adjacent(X,Y,X,Y+1):-col(Y+1).
adjacent(X,Y,X-1,Y):-row(X-1).
adjacent(X,Y,X+1,Y):-row(X+1).

path(0,0) :- not black(0,0).
path(0,1) :- not black(0,1).
seed(0,0).
seed(0,1).
path(X,Y) :- not black(X,Y), not seed(X,Y), adjacent(X,Y,Z,T), path(Z,T).

:- not black(X,Y), not path(X,Y).