@rot_mat

##</code><code>##

$rot_mat[0][0] = 'foo';

##</code><code>##

return \@rot_mat;

##</code><code>##

my $aref = &first_sub();

##</code><code>##

my $bar = $aref->[0]->[0];
# hard to read

##</code><code>##

my $baz  = $aref->[0];
my $quux = $aref->[1];
# now $baz is a reference to the anonymous array Perl created 
# for the first element of @rot_mat when you assigned a value
# to $rot_mat[0][0] in the first sub

say 'yep' if $baz->[0] eq 'foo';

##</code><code>##

foreach my $anon_array ( @{ $aref } ) { # dereference the main array
  foreach my $value ( @{ $anon_array } ) { # dereference the anon array 
    say 'yep' if $value eq 'foo';
  }
}

##</code><code>##