my @a = ( 1, 4, 9, 16);  # squares
my @b = ( 1, 8, 27, 64); # cubes
my @c = ( \@a, \@b );    # two arrays

my $d = \@a;
my $e = \@c;

# OK: @a is an array
print $a[0];

# Wrong: $d is a reference, not an array!
print $d[0];

# OK: Both of these are fine, though
print $d->[0];
print $$d[0];

# with multiple subscripts:
print $e->[0]->[0];
print $e->[0][0];    # same as above, since -> is optional between subscripts
print $$e[0][0];     # also same as above