DECLARE SUB SWEP (i!, j!)
DECLARE SUB P (k!)
CLS

DIM SHARED n
DIM SHARED x AS STRING
x = "1234"
n = LEN(x)
CALL P(1)
END

SUB P (k)
   IF k = n THEN
      PRINT x
   ELSE
      FOR i = k TO n
         SWEP k, i
         CALL P(k + 1)
         SWEP k, i
      NEXT i
   END IF
END SUB

SUB SWEP (i, j)
   DIM a AS STRING
   DIM b AS STRING
   a = MID$(x, i, 1)
   b = MID$(x, j, 1)
   MID$(x, i, 1) = b
   MID$(x, j, 1) = a
END SUB

DECLARE FUNCTION SUM$ (x$)
DECLARE FUNCTION f! (s1$, s2$)
CLS
DIM n  AS STRING
DIM n1 AS STRING
DIM n2 AS STRING

n1 = "111222"
n2 = "222111"
PRINT n1

DO
   n = SUM(n1)
   IF f(n, (n2)) THEN PRINT n
   n1 = n
LOOP UNTIL n = n2
END

FUNCTION f (s1 AS STRING, s2 AS STRING)
   DIM s AS STRING

   FOR i = 1 TO LEN(s1)
      s = MID$(s1, i, 1)
      k = INSTR(s2, s)
      IF k THEN MID$(s2, k, 1) = " "
   NEXT i

   s = LTRIM$(s2)
   IF s = "" THEN f = -1 ELSE f = 0
END FUNCTION

FUNCTION SUM$ (x AS STRING)
   DIM s AS STRING

   FOR i = LEN(x) TO 1 STEP -1
      s = MID$(x, i, 1)
      IF s = "2" THEN
         MID$(x, i, 1) = "1"
         GOTO 100
      ELSE
         MID$(x, i, 1) = "2"
         SUM = x
         EXIT FUNCTION
      END IF
100
   NEXT
END FUNCTION