For more information about countable and uncountable sets, see books about "Analysis" (as advanced calculus is called). For example, Introductory Real Analysis, by A.N. Kolmogorov and S.V. Fomin (see ...

A noun is a thing, e.g. cat, room, exam. Most of the time, we can talk about how many of these things we have: Bobby has three cats at home! It’s amazing how many rooms are empty in our school. I have ...