DB<26>  @a = (2 .. 9);

  DB<27>  @i = (2, 3, 5);

  DB<28>  @a[@i] = ()

  DB<29>  @b = grep defined, @a;

  DB<30> x @a
0  2
1  3
2  undef
3  undef
4  6
5  undef
6  8
7  9
  DB<31> x @b
0  2
1  3
2  6
3  8
4  9
  DB<32>
...
  DB<65> p exists $a[0]
1
  DB<66> p defined $a[0]

  DB<67>