% original version at http://www.csupomona.edu/~jrfisher/www/geolog/mb.in
% problem from Manthey/Bry

:- op(1200,xfx,':=').
:- op(1199,xfx,'=>').

:- dynamic(p/2).
:- dynamic(q/2).
:- dynamic(dom/1).
:- dynamic(answer/1).

flag(keywords).
flag(quiet).
flag(quick).

%domain elements a,b,c
dom(a). dom(b). dom(c). dom(d).

[p_total] := p(a,b) => answer(p(a,b)).
[q_total] := q(c,d) => answer(q(c,d)).
[] := answer(_) => goal.

[sym_p,X,Y] := p(X,Y) => p(Y,X).
% [sym_q,X,Y] := q(X,Y) => q(Y,X).
[trans_p,X,Y,Z] := p(X,Y),p(Y,Z) => p(X,Z).
[trans_q,X,Y,Z] := q(X,Y),q(Y,Z) => q(X,Z).

[p_or_q,X,Y] := dom(X),dom(Y) => p(X,Y);q(X,Y).