-2/3 plus 1/4 = -5/12

**** BEGIN HEAP DUMP ****
first_free = 3

  0: -1  2  3
  1: 1  1  4
  2: -1  5  12
  3: 0  0  4
  4: 0  0  5
  5: 0  0  6
  6: 0  0  7
  7: 0  0  8
  8: 0  0  9
  9: 0  0  10
**** END HEAP DUMP ****

**** BEGIN HEAP DUMP ****
first_free = 1

  0: -1  2  3
  1: 0  0  3
  2: -1  5  12
  3: 0  0  4
  4: 0  0  5
  5: 0  0  6
  6: 0  0  7
  7: 0  0  8
  8: 0  0  9
  9: 0  0  10
**** END HEAP DUMP ****

**** BEGIN HEAP DUMP ****
first_free = 5

  0: -1  2  3
  1: 1  8  42
  2: -1  5  12
  3: 1  17  96
  4: 1  247  672
  5: 0  0  6
  6: 0  0  7
  7: 0  0  8
  8: 0  0  9
  9: 0  0  10
**** END HEAP DUMP ****