I have as facts these (el stands for elephant):
el(Sam) el(Clyde) el(Oscar)
pink(Sam)
gray(Clyde) likes(Clyde, Oscar)
pink(Oscar)Vgray(Oscar) likes(Oscar, Sam)
Now, I want to prove(?) that: Some gray elephant likes some pink elephant, which translates to: (exists x)(el(x) /\ gray(x) /\ (exists y) (el(y) /\ pink(y) /\ likes(x, y)). So, we need to take its negation and resolve(?) it into the basis, in order to reach void(?).
The negation is (will use ~ to show negation):
~el(x) V ~gray(x) V ~el(y) V ~pink(y) V ~likes(x, y)
The way I see it, I shall assign x and y values (Sam, Clyde or Oscar) and insert the later statement in the base, to "kill" the facts that lie there already.
My attempt:
I set x = Clyde, y = Oscar, which gave me:
~el(Clyde) V ~gray(Clyde) V ~el(Oscar) V ~pink(Oscar) V ~likes(Clyde, Oscar)
which if I put into the base, "kill" their "pairs" and the base becomes:
el(Sam)
pink(Sam)
gray(Oscar) likes(Oscar, Sam)
and now what? We run out of elephants!
Ideally, I would like to have x' = Oscar, y' = Sam, so that I would get:
~el(Oscar) V ~gray(Oscar) V ~el(Sam) V ~pink(Sam) V ~likes(Oscar, Sam)
which would go into the base and kill everything, but ~el(Oscar) would still be alive! How should I proceed?
Follow-up question:
Base:
a
b
c V d
and then I put into the bases ~a/\~b/\~c/\~d. Everything in the base will be vanished in the same way? I mean wouldn't the V operator affect things?
You could have something like this:
el(sam).
el(clyde).
el(oscar).
pink(sam).
grey(clyde).
likes(clyde,oscar).
likes(oscar,sam).
canbe(oscar,grey).
canbe(oscar,pink).
gelephant_likes_pelephant(GE,PE):-
grey(GE),el(GE),
pink(PE),el(PE),
likes(GE,PE).
gelephant_likes_pelephant(GE,PE):-
canbe(GE,grey),el(GE),
pink(PE),el(PE),
likes(GE,PE).
gelephant_likes_pelephant(GE,PE):-
grey(GE),el(GE),
canbe(PE,pink),el(PE),
likes(GE,PE).
Qs:
?- gelephant_likes_pelephant(GE,PE).
GE = oscar,
PE = sam ;
GE = clyde,
PE = oscar.
You have to be careful how you use a predicate like canbe/2. As it is saying oscar can be grey or pink. Then my query is saying which grey elephants like which pink elephants, the answer can be interpreted as: IF oscar is a grey elephant THEN oscar likes sam OR IF clyde likes oscar THEN oscar is a pink elephant.