Hi Marc,

> I did not thought that Boolean operations worked with open curves.

Yeah there are several situations where open curves can be used.

Another one is they can be the objects that get cut by closed curves in a difference or intersection command.

Like for example here are some open curves (lines) that cross over some closed curves:



You can select those open curves and then do a difference or intersection with the closed curves.

Here is difference:



Here is intersection:




Another thing that can work is to have a grid of crossing open curves, like this:



Then boolean union should be able to form closed curves for each cell (I dragged the result curves a little bit apart for illustration):




However, the curve booleans can tend to be a bit buggier than the regular booleans, you may sometimes run into a stray edge that needs to be cleaned up with the unioning.

- Michael