my @site1 = qw( AATKKM aatkkm );
    my @site2 = qw( GGGGGG gggggg );

    my %counts;

    seq_foreach_from_spec( [ \(@site1, @site2) ],
        sub {
            seq_foreach(
                seq_zip( ( map seq(split//), @_ ) ),
                sub { $counts{"@_"}++ }
            ) 
        }
    );

    print Dumper(\%counts), "\n";

    # { 'K G' => 2, 'A G' => 2, 'm g' => 1, 'a g' => 2,
    #   'A g' => 2, 'M G' => 1, 'k g' => 2, 'k G' => 2,
    #   'T G' => 1, 'a G' => 2, 'm G' => 1, 't G' => 1,
    #   'K g' => 2, 'M g' => 1, 't g' => 1, 'T g' => 1 }