$ perl -le'{
    my @a;  $a[15][0];
    print "After autovivification:      ",
        exists($a[14])  || 0,
        exists($a[15])  || 0,
        defined($a[14]) || 0,
        defined($a[15]) || 0;
}{
    my @a;  $a[15] = [];
    print "After explicit vivification: ",
        exists($a[14])  || 0,
        exists($a[15])  || 0,
        defined($a[14]) || 0,
        defined($a[15]) || 0;
}'
After autovivification:      0101
After explicit vivification: 0101