Question

What is the uppercase ‘N’ before prolog term mean?

such as the P in imp becomes NP in not？

imp(P,Q,Y) :- not(P,NP),or(NP,Q,Y).

NP means negation of P in prolog?

N is a kind of built in function in prolog?

Thanks a lot.

Answer 1

It has no special meaning. The term NP, which starts with an upper case, means that it is a variable (it could start with any upper case letter).

The way I read your procedure:

imp(P,Q,Y) :- not(P,NP),or(NP,Q,Y).

it means: ‘ to get P implies Q onto variable Y’ we call procedure not/2 to get the negation of input P, and then we call procedure or/3 which computes “not P or Q” onto variable Y. Of course you have somewhere defined procedures not/2 and or/3