/* natural numbers in axiomatic set theory 
   2005-11-22, Kazunori Ueda
   
   When run with LMNtal Java in the interactive
   mode (i.e., not under LMNtalEditor IDE),
   run with the --remain and --interpret option and
   give as many more inc's as you like!
*/

% The successor of a set S is S U {S}.  So, for
% each inc message, S will evolve into its new
% version by including the old S as a new member.
inc, {$p[]} :- {$p[], {$p[]}}.

% we have a zero initially
{}.

% specify several inc's below
inc.  inc.  inc.
