% file: tutors.pro 
% author: Robert Keller 
% purpose: Prolog tutorial example involving tutors, dorms, etc. 

:- ensure_loaded('enumerate.pro'). 

% lives(N, D) means that person named N lives in dorm D 
lives('John', 'East'). 
lives('Naima', 'South'). 
lives('Alice', 'West').
lives('Toshiko', 'East'). 
lives('Roy', 'North'). 
lives('Albert', 'South'). 

% takes(N, D, C) means that person named N takes course C in department D 

takes('John', 'CS', 60). 
takes('Naima', 'CS', 60).
takes('Alice', 'CS', 60). 
takes('Toshiko', 'CS', 5). 
takes('Albert', 'CS', 60). 
takes('Roy', 'Math', 55). 
takes('Naima', 'Math', 55).
takes('Alice', 'Math', 70). 
takes('Toshiko', 'Math', 80).
takes('Albert', 'Math', 55). 

% tutors(N, D, C) means that person named N tutors course C in department D 

tutors('John', 'CS', 5). 
tutors('Naima', 'CS', 5). 
tutors('Roy', 'Math', 3). 
tutors('Alice', 'Math', 55).
tutors('Albert', 'Math', 4). 

% livesInEast(X) means that person named X lives in east. 

livesInEast(X) :- lives(X, east). 

% canTutor(X, Y) means that person X can tutor person Y (because X is tutoring 
% a course that Y is taking) 

canTutor(X, Y) :- tutors(X, Dept, Number), takes(Y, Dept,
Number). 

% knows(X, Y) means that person X knows person Y 
knows(X, Y) :-knows(X, Y, _). 

% knows(X, Y, R) means that person X knows person Y for reason R 
% For example, R can be 'living' because both live in the same dorm, 
% or 'tutoring' because Y can tutor X. 

knows(X, Y, living) :-
    lives(X, Z), lives(Y, Z). 

knows(X, Y, tutoring) :- 
    canTutor(Y, X).