Hi, I propose to remove the fastcsg experimental option. There are three problems with fastcsg: * Robustness: It is not as robust as manifold and must fallback to Nef polyhedron for these degenerate cases. User may also turn on both fastcsg and manifold and get weird result/performance. * Performance: There are cases in which fastcsg is slower than Nef polyhedron, and it is slower than manifold. (https://gist.github.com/ochafik/70a6b15e982b7ccd5a79ff9afd99dbcf#results) * Maintenance issue: Half of the files in |src/geometry/cgal| are about fastcsg, retiring fastcsg may allow us to simplify a lot of the logic. Please let me know if you have any comments about this. Feel free to reply to this thread or comment on https://github.com/openscad/openscad/issues/4870 Cheers, John