/*  Filename:  antest.pro

    Author:  Br. David Carlson

    Date:  December 17, 1999

    This program creates a small set of facts and rules on who is the ancestor
    of whom.  This program prints the complete set of who is an ancestor of
    whom when started with the goal:  go.
*/

/*  Note that ancestor(A, B) means that A is an ancestor of B. */
ancestor(bob, susan).
ancestor(A, X) :- parent(A, X).
ancestor(A, X) :- parent(A, C), ancestor(C, X).

/* Note that parent(P, C) means that P is a parent of C. */
parent(fred, sally).
parent(tina, sally).
parent(sally, john).
parent(sally, diane).
parent(sam, bill).

go :- ancestor(Anc, Off), write(Anc), write(' is an ancestor of '),
   write(Off), nl, fail.
go.