How to create a list from facts in Prolog?

Question

There are these facts:

man(john).
man(carl).
woman(mary).
woman(rose).

I need to create the predicate people(List), which returns a list wi

Answer 1

Using findall/3:

people(L) :- findall(X, (man(X) ; woman(X)), L).

?- people(X).
X = [john, carl, mary, rose].

Answer 2

Here we go:

person(anne).
person(nick).

add(B, L):-
    person(P),
    not(member(P, B)),
    add([P|B], L),!.

add(B, L):-
    L = B,!.

persons(L):-
    add([], L).