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107 ira 1 
/* ca2.pl
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   Cryptarithmetic:
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   forbids the same digit being used more than once */
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ca(L) :- write('     S  E  N  D  M  O  R  Y'),
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         L = [S,E,N,D,M,O,R,Y],
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         col( 0,D,E,Y,C1,L),
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         col(C1,N,R,E,C2,L),
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         col(C2,E,O,N,C3,L),
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         col(C3,S,M,O,C4,L),
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         col(C4,0,0,M, 0,L).
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col(Ci,X,Y,Z,Co,L) :- carry(Ci),
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                      free_digit(X,L),
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                      free_digit(Y,L),
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                      free_digit(Z,L),
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                      carry(Co),
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                      sum(Ci,X,Y,Z),
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                      carry(Ci,X,Y,Co).
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sum(Ci,X,Y,Z) :- Z is (Ci+X+Y) mod 10.
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carry(Ci,X,Y,Z) :- Z is (Ci+X+Y) // 10.
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digit(0).
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digit(1).
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digit(2).
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digit(3).
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digit(4).
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digit(5).
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digit(6).
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digit(7).
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digit(8).
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digit(9).
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carry(0).
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carry(1).
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free_digit(Dig,UsedList) :- var(Dig),
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                            digit(X),
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                            not_in(X,UsedList),
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                            Dig = X.
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free_digit(Dig,_) :- nonvar(Dig).
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not_in(_,[]).
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not_in(D,[H|T]) :- var(H), not_in(D,T).
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not_in(D,[H|T]) :- nonvar(H), D \= H, not_in(D,T).
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