Hi Pilou, Ok - so no green markers or + signs needed - good! :)

Just in general it is more normal to avoid creating those kinds of twisted surfaces. Those surfaces are "self-intersecting" - they fold back and forth over on top of themselves and that means they will have a kind of inconsistent surface normal which will make a lot of problems with more advanced calculations like surface intersections used in booleans or things like that.

So although it's possible to create something like that just to look at it, it's not a good practice for a good clean and proper model structure.

- Michael