# שלום כיטה א!

The main feature that distinguishes the Calculus (or Mathematical Analysis) from other branches of mathematics is the repeated use of infinite constructions and processes. Without infinity even the simplest things, like the decimal representation of the simple fraction $\frac13=0.333333\dots$ becomes problematic.

Yet to deal with infinity and infinite constructions, we need to make precise our language, based on the notions of sets and functions (maps, applications, – all these words are synonymous).

Look at the first section of the lecture notes here.

You are most welcome to start discussions in the comments to this (or any other) post. Don’t be afraid of asking questions that may look stupid: this never harms! Write in any language (besides Hebrew/English, I hope that Ghadeer will take care of questions in Arabic, and I promise to deal with French/Spanish/Catalan/Italian/Russian/Ukrainian questions) 😉 Subscribe for updates on this site with your usual emails, to be independent from any dependence 😉

Looking forward for a mutually beneficial interaction in the new semester!

## Sunday, October 27, 2013

### Lectures 1 and 2 (Oct. 22 & 29, 2013)

We start our course by first carefully walking in a zoo with several surprising, wonderful or dangerous beasts, all caught in the Jungle of Infinity. To tame them, we need to wear some protective gear made of ironclad formulas, operate from the safety of well defined sets and use the tools provided by functions 😉

The lecture notes (considerably updated and revised in comparison with the previous years) can be found here. Please report typos, errors and complain about obscure instances in the comments.

Please pay attention to the problems scattered over the text: they are mostly for self-control, but if you are not sure, you may write your solutions and submit them (e.g., in the comments to this post, but also directly to Inna, if you want to keep it private).

## Infinity: first accurate steps

1. Finite and infinite subsets of $\mathbb N$.
2. Admissible infinite operations: infinite unions and intersections. Quantifiers.
3. “Small” and “large” infinite subsets of $\mathbb N$.
4. One-to-one maps as the means of comparison between various infinite sets.
5. The first “paradox”: $\mathbb N\times\mathbb N\simeq\mathbb N$.