collapseos/blk/434

: MOVE ( a1 a2 u -- )
    ( u ) 0 DO
        SWAP DUP I + C@   ( a2 a1 x )
        ROT SWAP OVER I + ( a1 a2 x a2 )
        C!                ( a1 a2 )
    LOOP
    2DROP
;
: FILL ( a n b -- )
    SWAP 2 PICK + ( a b a+n ) ROT ( b a+n a ) DO ( b )
        DUP I C!
    LOOP
;
: DELW 1- 0 SWAP C! ;
: PREV 3 - DUP @ - ;