\ --- 1 ---

: KEUS  ( n ch -- nr )
  TUCK +                  \ ch  ch+n
  DUP                     \ Dummy
  BEGIN DROP              \ Vorige key
        KEY
        DUP 2OVER WITHIN
  UNTIL NIP
  - NEGATE ;


\ --- 2 ---

: KEUS  ( n ch -- nr )
  TUCK +                  \ ch  ch+n
  BEGIN KEY
        DUP 2OVER WITHIN
        AND ?DUP          \ 0 | key key
  UNTIL NIP
  - NEGATE ;