Welcome to SWI-Prolog (Multi-threaded, 64 bits, Version 6.6.5)
Copyright (c) 1990-2013 University of Amsterdam, VU Amsterdam
SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to redistribute it under certain conditions.
Please visit http://www.swi-prolog.org for details.

For help, use ?- help(Topic). or ?- apropos(Word).


true.

Stack: [10,9,8,7,6,5,4,3,2,1,1,2,3,4,5,6,7,8,9,10]
Result: [1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10]; OK
true.


% halt