human(jack).
income(jack, 480).

human(jones).
income(jones, 20).

human(joe).
income(joe, 1000).

human(jeremy).
product(jeremy).

product(grapes).
cost(grapes, 5).

product(pasta).
cost(pasta, 1).

product(car).
cost(car, 400).
likes(jack, pasta).
likes(jones, car).
likes(joe, car).
can_afford(X, Y) :- 
  income(X, Income), 
  cost(Y, Cost), 
  Income > Cost.
will_buy(X, Y) :- 
  human(X), 
  product(Y), 
  likes(X, Y), 
  can_afford(X, Y).