/*
NOTE: a query is a goal to prove
?- Head.
*/
% include database
:- include('db.pl').
% green is a color
?- color(green). % true.
% michael is male
?- male(michael). % true.
% a query fails if goal is not provable
% even if true
?- color(boat). % false. (this is correct)
?- color(black). % false. (but should be true, description is incomplete)
% equality
?- =(a, b). % false.
?- a = b. % false.
?- a = a. % true.
% note: atom = atom, but atom /= list
?- 'michael' = michael. % true.
?- "michael" = michael. % false.
% disequality
?- "michael" \= michael. % true.
% greater/ less than or equal
?- 5 >= 10. % false.
?- 5 =< 10. % true.
% assignment
?- X = 5. % X = 5.
% assignment and conditional
?- X = 5, X =< 10. % false.
% substitution
?- expression(10, Y) = expression(X, 2). % Y = 2, X = 10.
% compound queries: all goals need to be true
?- male(michael), friend(michael, adam). % true
% queries using logical variables
?- color(X). % X = red ; X = green ; X = blue ;
?- person(michael, nationality(X, Y)). % X = sweden, Y = swedish.
% anonymous variables (ignoring values)
?- person(X, nationality(sweden, _)). % X = michael
% conditional solutions
?- dif( f(g(X)), f(g(Y)) ). % dif(Y, X).