( compute factorial recursively )( take x as input, return x! and x as output ): fact-help  dup if    1 -			( leave x-1 on top )    fact-help		( leave x-1, [x-1]! )    1 +			( leave x, [x-1]!, x )    swap over swap	( leave [x-1]!, x, x )    *			( into x!, x )    swap		( into x, x! )  else    1 swap  then;: fact  fact-help  drop;: demo4  " 4 factorial is: " 4 fact . cr  " 6 factorial is: " 6 fact . cr;demo4