🚀 go-pugleaf

I am working my way through the Turbo Prolog tutorial, in attempt to learn
Prolog.  By the way, does anyone have any good textbook suggestions for a
quick, advanced introduction to Prolog?

Anyway, I am stuck on the use of the cut.  There is an exercise in the book
which requires the printing of a tournament between players.  Each player
should only be occur once.  Also, only those players in equal or lower
league may be challenged.  See the book for further info.  Somehow the 
cut is supposed to be the solution, but I don't see it.  The example 
below is as close as I have come, but it doesn't work.

/* exercise 2, tutorial III */

domains
  name=symbol
  league=integer
predicates
  tourney(name,name)
  partner(name,league,name)
  can_challenge (league,league)
  player(name,league)
  flag_end(name)
clauses
  player(tom,3).
  player(tim,3).
  player(tut,3).
  player(sue,2).
  player(sam,2).
  player(sis,2).
  player(joe,1).
  player(jim,1).
  player(jed,1).
  player(end,0).
  can_challenge(P,Q) :- P >= Q.
  tourney(X,Y) :- player(X,Xl),
                  partner(X,Xl,Y).
  partner(X,Xl,Y) :-
                    player(Y,Yl),
                    X <> Y,
                    can_challenge(Xl,Yl),
                    flag_end(Y).
  flag_end(P) :- P <> end,!.


Can anyone help me?


Kevin Buchs   3500 Zycad Dr. Oakdale, MN 55109  (612)779-5548
Zycad Corp.   {rutgers,ihnp4,amdahl,umn-cs}!meccts!zeke!kevin
-- 
Kevin Buchs   3500 Zycad Dr. Oakdale, MN 55109  (612)779-5548
Zycad Corp.   {rutgers,ihnp4,amdahl,umn-cs}!meccts!zeke!kevin