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Text File  |  1989-08-23  |  353 b   |  20 lines
  1. %  difference/3
  2.  
  3. difference([],_,[]).
  4. difference([X|Set1],Set2,Diff) :-
  5.    element(X,Set2), !,              % See element/2
  6.    difference(Set1,Set2,Diff).
  7.  
  8. difference([X|Set1],Set2,[X|Diff]) :-
  9.    difference(Set1,Set2,Diff).
  10.  
  11. %  element/2
  12.  
  13. element(X,[X|_]).
  14. element(X,[_|Set]) :-
  15.    element(X,Set).
  16.  
  17. % difference([1,2,3,4,5],[2,3,5,6],X).
  18.  
  19. % X = [1,4] 
  20.