muda's Journal

leave a Grothendieck universe
искрометный пассаж из википедии:

There is another approach to universes which is historically connected with category theory. This is the idea of a Grothendieck universe. Roughly speaking, a Grothendieck universe is a set inside which all the usual operations of set theory can be performed. For example, the union of any two sets in a Grothendieck universe U is still in U. Similarly, intersections, unordered pairs, power sets, and so on are also in U. This is similar to the idea of a superstructure above. The advantage of a Grothendieck universe is that it is actually a set, and never a proper class. The disadvantage is that if one tries hard enough, one can leave a Grothendieck universe.