@peterrowlett You don't have to explain everything you know about it, that is way too much. You only need to say what he can understand, that will suffice. There is a huge difference
What examples are there of non-principal proper filters, other than Frechet filters, or the set of neighborhoods of a point in a topological space, or the subsets of natural numbers that contain all multiples of a fixed number?
@ashkenegro Not at all. Numbers count. More people more trash, more CO2, more pollution. Whatever the race, people are always a load of logistic problems
3D solid, circular base, cross-sections are equilateral triangles perpendicular to the X axis, showing the two walls are subsets of slant parabolic cylinders going in opposite directions