sub intersect3 { 
	my ($a,$b,$c,$d) = map {($_->[0],$_->[1])} sort { $a->[0] <=> $b->[0] } ([@_[0,1]],[@_[2,3]]); 
	return ($b-$c)*($b>$c)-($b-$d)*($b>$d); 
	}