Split in two objects after difference

[iibPScheich]

Hello and thanks for your work,
I am struggling with a little problem.
Is it possible to split an object in two by building the difference with another object.

How can I split the green object in two CSGs? I want to keep the lower part.

Thanks.

[madhephaestus]

Make a much larger rectangle that encompases the upper section. Perform an intersection to make the upper shape and a difference to make the lower shape.