On Mar 21, 8:46 am, WM <mueck...@rz.fh-augsburg.de> wrote:
> My question remains: What is the subset of necessary lines?
There is no such thing as a necessary line. There is such a thing as a sufficient set of lines (all sufficient sets are composed entirely of unnecessary lines, which means that you can remove any finite set of lines from a sufficient set and get a different sufficient set of lines). The intersection of all sufficient sets is empty.