DEF fnx1 (x, y) = .836 * x + .044 * y
  DEF fny1 (x, y) = -.044 * x + .836 * y + .169
  DEF fnx2 (x, y) = -.141 * x + .302 * y
  DEF fny2 (x, y) = .302 * x + .141 * y + .127
  DEF fnx3 (x, y) = .141 * x - .302 * y
  DEF fny3 (x, y) = .302 * x + .141 * y + .169
  DEF fnx4 (x, y) = 0
  DEF fny4 (x, y) = .175337 * y
  SCREEN 12
  CLS
  p(1) = .4
  p(2) = .6
  p(3) = .8
  p(4) = 1!
  x = .1
  y = .3
  count = 0

  WHILE INKEY$ <> CHR$(13)
     PSET (10 + y * 600, 200 + x * 600)
     q = RND(1)
     k = 4
     count = count + 1
     LOCATE 1, 20: PRINT count;
     FOR i = 1 TO 3
         IF q < p(i) THEN k = i: i = 4
     NEXT i
     ON k GOSUB 10, 20, 30, 40
     x = x0: y = y0
  WEND
  dummy$ = INPUT$(1)
  CLS
  END

10 x0 = fnx1(x, y)
   y0 = fny1(x, y)
   RETURN
20 x0 = fnx2(x, y)
   y0 = fny2(x, y)
   RETURN
30 x0 = fnx3(x, y)
   y0 = fny3(x, y)
   RETURN
40 x0 = fnx4(x, y)
   y0 = fny4(x, y)
   RETURN