PR1 Solution Guide:
16 points overall; 1 point for each question

Ex1.1 [B]
(a) No
(b) X = pat ; 
(c) X = bob ; No
(d) X = bob Y = pat ; No

Ex1.2 [B]
(a) ?- parent( X,pat).
(b) ?- parent( liz,X).
(c) ?- parent( X,Y), parent(Y,pat).
  (or: ?- parent( Y,pat), parent( X,Y).

Ex1.3 [B]
(a) happy( X) :- parent( X,_).
(b) hastwochildren( X) :- parent( X,Y), sister( Z,Y).

Ex1.4[B]
grandchild( X,Y) :- parent( Y,Z), parent( Z,X).

Ex1.5[B]
aunt( X,Y) :- parent( Z,Y), sister( X,Z).
We do not consider aunts by marriage!

Ex1.6[B]
Yes, it is a correct definition.

Ex1.7[B]
(a) No backtracking
(b) No backtracking
(c) No backtracking, because of the order of clauses on pp.3-4
(d) Backtracking: parent(bob,ann) is tried first to solve the goal 
parent(bob,Y1), but it turns out to be a dead end!  Upon backtracking,
parent(bob,pat) is used, and that leads to the solution.