When reading the section Filling in the blanks in Prolog’s day 1, I decided to try
with the facts and rule from Basic Facts instead of the @food_type(What,meat)@ example.
To my surprise the answer was no.
After reading Day 3 Self-Study (where “problems” with Prolog’s “not expressions” are mentioned) I tried
friend1(X, Y) :- likes(X, Z), likes(Y, Z), \+(X = Y).
which works as expected. Nevertheless, I don’t understand why…
I think it would be helpful not to leave the reader alone here.
I’m reading P3.0.