sub common {
    my $num = @_;
    my (%common, %test);
    $_ = shift;
    @common{@$_} = () x @$_; # second use is scalar context
    while ( $_ = shift) {
        %test = ();
        @test{@$_} = () x @$_;
        delete @common{  grep { ! exists $test{$_} } keys %common};
    }
    [ [keys %common] x $num ];
}