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q(X,N):-X<9,N=0;A is abs(X mod 10-X//10 mod 10),Y is X//10,q(Y,M),N is A+M*10. r(X,N):-X<9,N=X;q(X,Y),r(Y,M),N is X+M. p(X):-r(X,N),write(N).