Subversion Repositories programming

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107 ira 1 
/* pair2.pl -- pairs of digits WITHOUT replacement */
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pair(L) :- L = [X,Y],
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           free_digit(X,L),
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           free_digit(Y,L).
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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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digit(0).
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digit(1).
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digit(2).
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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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