error: element number 1 undefined in return list
error: called from
    ex1_run at line 2 column 16

   0   1   2   3   4   6   7   8   9
    9    4   15    4    4    2    4    9    8

     0     1     2     3     4     6     7     8     9

     9     4    15     4     4     2     4     9     8