Nov 12, 2003
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<class handled by Saverio Perugini>

Returned HW7.

Answered questions on HW8.

Announced HW9.

Answered questions on P3.

Discussed tracing Prolog programs involving cuts! including the
following example.

parent(X, Y) :- father(X, Y).
parent(X, Y) :- mother(X, Y).

is same as

parent(X, Y) :- father(X, Y); mother(X, Y).

parent(X, Y) :- father(X, Y), !.
parent(X, Y) :- mother(X, Y).

father(linus, lucy).
father(andrew, matthew).
mother(ruth, bob).

?- parent(X, Y).

X = linus
Y = lucy ;

No.

--

parent(X, Y) :- father(X, Y).
parent(X, Y) :- mother(X, Y).

father(linus, lucy) :- !.
father(andrew, matthew).
mother(ruth, bob).

?- parent(X, Y).

X = linus
Y = lucy ;

X = ruth
Y = bob ;

No

--

parent(X, Y) :- !, father(X, Y).
parent(X, Y) :- mother(X, Y).

father(linus, lucy).
father(andrew, matthew).
mother(ruth, bob).

?- parent(X, Y).

X = linus
Y = lucy ;

X = andrew
Y = matthew ;

No