my @array;
if (defined $array[20]) { }                           # no autovivification, thus
if (defined $array[20]) { warn "[20] does exist!" }   # no warning

##</code><code>##

my @array;
if (exists $array[20]->[42]) { }
if (exists $array[20]) { warn "[20] does exist!" }

__END__
[20] does exist! at ./808911.pl line 5.