2
votes
1answer
60 views

Definition of direct products of two cones or of two convex subsets?

When reading a comment after this reply, I was wondering what the definitions of direct product of two cones? More generally, what is the direct product of two convex subsets? This case is what I ...
7
votes
1answer
266 views

Making sense out of “field”, “algebra”, “ring” and “semi-ring” in names of set systems

There are some set systems with algebraic titles, such as "field", "algebra", "ring" and "semi-ring" (and possibly other titles), in their names. Examples are a sigma field (aka sigma algebra, ...