Working on Introduction to Smooth Manifolds by Loring Tu (AKA $L^2$) with Charles.

## 1.1: Smooth vs. Analytic functions

I don’t yet see why this distinction is the first thing the book talks about.

Smooth functions are infinitely differentiable. Analytic functions are even stronger since they equal their Taylor series.

I already hate the convention of writing a point $p$ in coordinates with superscripts $(p^1 \dots p^n)$. I prefer subscripts and slice notation: $p := p_{1:n}$.

Bump functions are cool, since you can create a smooth function that’s totally flat outside an arbitrarily small region.

Charles pointed out that non-analytic smooth functions are physically because they change their values in a finite amount of time but can have 0 derivative of every order.

## 1.2: Taylor’s Theorem with Remainder

Smooth functions can be approximated well by a Taylor series.

This section basically derives the Taylor formula.

Here’s the ending note:

NOTATION. It is customary to write the standard coordinates on $\mathbb{R}^2$ as $x, y$, and the standard coordinates on $\mathbb{R}^3$ as $x, y, z$.

In case you didn’t know that. And yet are reading a book about smooth manifolds.