@union = @intersection = @difference = ();
    %count = ();
    foreach $element (@array1, @array2) { $count{$element}++ }
    foreach $element (keys %count) {
        push @union, $element;
        push @{ $count{$element} > 1 ? \@intersection : \@difference }, $element;
    }

##</code><code>##

sub intersection{
 my(%count,@res);
 for(map @$_,@_){$count{$_}++}
 for(keys %count){push @res,$_ if $count{$_}==@_}
 @res;
}
@a=intersection(\@b,\@c,\@d);