directlyIn(olga, katarina).
directlyIn(natasha, olga).
directlyIn(irina, natasha).
contains(Doll1, Doll2) :- directlyIn(X, Doll1), contains(X, Doll2).
contains(Doll1, Doll2) :- directlyIn(Doll2, Doll1).
/* Test */
test_answer1 :-
directlyIn(irina, natasha),
writeln(‘OK’).
test_answer2 :-
\+ directlyIn(irina, olga),
writeln(‘OK’).
test_answer3 :-
contains(katarina, irina),
writeln(‘OK’).
test_answer4 :-
contains(katarina, natasha),
writeln(‘OK’).