Fubini's theorem
http://dmentrard.free.fr/GEOGEBRA/Maths/FubiniiMD.html
[url=http://dmentrard.free.fr/GEOGEBRA/Maths/FubiniiMD.html]http://dmentrard.free.fr/GEOGEBRA/Maths/FubiniiMD.html[/url]
Information: Fubini's theorem