isfizz(N) :- mod(3, N) =:= 0.
isbuzz(N) :- mod(5, N) =:= 0.
isfizzbuzz(N) :- mod(15, N) =:= 0.

dofizzbuzz(N, F) :- isfizzbuzz(N), F = fizbuzz.
dofizzbuzz(N, F) :- isbuzz(N), F = buzz.
dofizzbuzz(N, F) :- isfizz(N), F = fizz.
dofizzbuzz(N, F) :- F = N.