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>

##</code><code>##


  DB<40>  @a = (0..4)

  DB<41>  delete @a[0,2,4]

  DB<42>  p exists $a[0]

  DB<43>  p exists $a[1]
1
  DB<44>  x @a     # shortened
0  undef
1  1
2  undef
3  3
  DB<45>  p scalar @a
4
  DB<46>

##</code><code>##

DB<56>  x @a
0  undef
1  1
2  undef
3  3
  DB<57>  $a[5] = undef

  DB<58>  x @a
0  undef
1  1
2  undef
3  3
4  undef.  # gap 
5  undef.  # value
  DB<59>  p exists $a[4]

  DB<60>  p exists $a[5]
1
  DB<61>