sub mk_kv; sub reverse_hoa;

sub mk_kv {
    return $_[0] => [ @_[1 .. $#_] ];
}

sub reverse_hoa {
    my %hoa = @_;
    my %reversed;
    for my $key ( keys %hoa ) {
        for my $value ( @{$hoa{$key}} ) {
            push @{$reversed{$value}}, $key
        }
    }
    return %reversed;
}