thanxs Michael,

Great explanation! I noticed something in your example after trying it myself. If I use boolean>diff or merge to split the sphere and then boolean>union the resulting solids, I get back the whole sphere without a cut line. However, when I do a edit>trim on the sphere and then a edit>join, the trim line stays. Is this the correct/expected behavior? Is there and untrim-like command in MoI.

Also, is the boolean union really the entire sphere or is there a hidden split line that is not displayed?

Its very interesting, Im learning a lot here. thanxs!

--Luis