permission error

[Cliff Bender]

Hi again,

I'm taking an example from http://www.csupomona.edu/~jrfisher/www/prolog_tutorial/3_3.html
and have the following in the file meta_interp.pl

clause_tree(true) :- !.      /* true leaf */
clause_tree((G,R)) :-
   !,
   clause_tree(G),
   clause_tree(R).           /* search each branch */
clause_tree(G) :-
   clause(G,Body),
   clause_tree(Body).        /* grow branches */

I then run

clause_tree(member(a,[a,b,c])).

and get the following error

uncaught exception: error(permission_error(access,private_procedure,member/2),clause/2)

Does
anybody have any idea? member is a built-in with gprolog (i know this
because i tried to define one, and it says so) and i'm not calling
clause/2, but clause_tree/2.

thanks,
Cliff