om(alin). om(adina). om(cristi).
place(alin, adina). place(adina, cristi).

fericit(X) :- om(X), om(Y), place(Y, X).

factorial(0,1).
factorial(N, Result) :- 
	N > 0,
	Prev is N-1,
	factorial(Prev, F),
	Result is N*F.