CODEWITHSUNDEEP
listprologsetset-difference
user3533469
user3533469

Reputation: 59

Prolog Difference of 3 sets (S1\S2)\S3

i have this working predicate for difference of 2 sets

difference([],Y,[]).
difference([X|R],Y,Z) :-
    member(X,Y),
    !,
    difference(R,Y,Z).
difference([X|R],Y,[X|Z]) :-
    difference(R,Y,Z).

But i would like to make similar thing for 3 sets and i can't figure it out difference(S1,S2,S3,result) resulting in (S1\S2)\S3.

Upvotes: 2

Views: 288

Answers (1)

willeM_ Van Onsem
willeM_ Van Onsem

Reputation: 476594

Well you basically already say it yourself: take the formula (S1\S2)\S3, substitute S1\S2 by T1 (a temporary), then the resulting formula is T1\S3.

So now put this into code:

difference(S1,S2,S3,Result) :-
    difference(S1,S2,T1),       %T1 = S1\S2
    difference(T1,S3,Result).   %Result = T1\S3=(S1\S2)\S3

Upvotes: 1

Related Questions