sub are_hashes_equal($$) {

        my ($a, $b) = @_;  # hashrefs

        # number of keys in hashes must be the same

        return 0 unless keys %$a == keys %$b;

        # and each key-value pair in %$a must have an
        # identical key-value pair in %$b

        while (my ($key_a, $val_a) = each %$a) {
            return 0 unless exists $b->{$key_a}
                            && $b->{$key_a} eq $val_a;
        }

        return 1;
    }