Hi PaQ,

> Is it 'normal' that when I try to trim A by B

Currently it is - every closed curve, including trim curves has a "seam" point where the start of the curve touches the end of the curve.

It is not unusual for chunks of the NURBS library code to treat a closed curve or edge the same as an open one when it gets diced into pieces. That usually means that there will be a couple of extra small segments created, one from the "start" of the closed curve to the first cutting point, and then another one from the last cutting point to the "end" of the closed curve.

I've tried to clean this up in several places already, like when you trim a circle curve you don't get an extra point at the seam because of some extra work that I did to fix that case up.

I do expect to be able to improve the surface edge case as well, that is actually bumped up pretty high on the todo list. It can also help fillets to avoid diced up edges as well.

- Michael