Many thanks
it's always good to see many possible version of a same problem
As you say maybe not more fast (if the object is very complex), and maybe more perilous in the extractions but working also :)

I have first thinking of just draw a triangle, extrude it, but the boolean result union with the first object don't work :(
But maybe I have another idea :)

All of that is of course a conceptual subject :)