swap 2dup second member? [ 2drop 2 ] [ first >= [ 1 ] [ 0 ] if ] if ;
: shift-stack ( n stack -- stack' )
- first2 pick '[ _ + ] map [ 0 >= ] filter pick 0 max iota sets:union
+ first2 pick '[ _ + ] map [ 0 >= ] filter pick 0 max <iota> sets:union
[ + ] dip 2array ;
! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!