collapseos/blk/439

: _|&
    ( n1 n2 cell )
    >R >R DUP R> R>          ( n1 n1 n2 cell )
    @ EXECUTE                ( n1 f )
;

( n1 f n2 -- n1 f )
: _|
    CREATE , DOES>
    ( n1 f n2 cell )
    ROT IF 2DROP 1 EXIT THEN ( n1 true )
    _|&
;