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A slice of an empty list is still an empty list. Thus:
    @a = ()[1,0];           # @a has no elements
...
More generally, a slice yields the empty list if it indexes only beyon
+d the end of a list:
    @a = (1)[  1,2];        # @a has no elements
    @b = (1)[0,1,2];        # @b has three elements

use strict;
use warnings;
...
          'world' => undef,
          'goodbye' => undef
        };

$VAR1 = {
          'mars' => 4,
          'hello' => 1,
        };

my @arr = (10, 20, 30, 40);
...
          40
        ];