sub read_dt2 {
    my ($path) = @_;
    open my $IFH, '<', $path
        or die "cannot open file '$path': $!";

    my %mysterious_hash_keyed_by_nucleotide;
    for my $nucleotide ( qw( A C G T ) ) {
        local $_ = <$IFH>;
        $mysterious_hash_keyed_by_nucleotide{$nucleotide} = [split];
    }
    close $IFH
        or warn "cannot close file '$path': $!";
    return \%mysterious_hash_keyed_by_nucleotide;
}