This repository contains a customization of Typst's standard AMS template so that it looks like TeX's amsart
using the fullpage
package.
We created this to match the common
#import "amsart.typ": *
#show: ams-article.with(
title: "On discrete Fourier analysis
and applications",
authors: (
(
name: "Letícia Mattos",
organization: [IMPA],
location: [Rio de Janeiro, RJ, Brasil],
email: "[email protected]"
),
),
abstract: [In this short note we introduce a few tools in discrete Fourier analysis and prove Meshulam and Roth's theorem.
These notes are based on a minicourse given by Victor Souza at IMPA, summer 2024.],
bibliography-file: "refs.bib",
)
#show: ams-stmt-rules
#show: ams-general-rules
= Lecture 1: Fourier analysis and arithmetic progressions
<introduction>
The goal of this lecture is to introduce the definitions and ideas required to prove
#citeauthor[@Me95]'s theorem @Me95, the analogue of the theorem by #citet[@Ro53] for finite fields $FF_q^n$.
The *Physical space basis* is the set of functions $delta_z: G -> CC$ defined by
$ delta_z (x) = cases(1 "if" x in A, , 0 "otherwise".) $
#definition[
A character of $G$ is a group homomorphism $chi: G -> CC^*$. In other words, a character is a function $chi$ such that $chi(x+y) = chi(x) chi(y)$ for all $x,y in G$.
]
The set of characters also defines a group, called the *dual group* of $G$ and denoted by $hat(G)$.
A special character is the identity function $chi_0(x) = 1$ for all $x in G$.
Now, our next goal is to prove the following theorem.
#theorem[
The set of characters of $G$ forms an orthonormal basis of $L_2(G)$.
]<characters-basis>
The first step is to show that the characters are indeed orthonormal is to prove the following lemma.
#lemma[
Let $chi eq.not chi_0$ be a character of $G$. Then,
$ EE_(x in G) chi(x) = 0. $
]<characters-orthonormal>
#proof[
Let $chi$ be a character of $G$ different from $chi_0$. As $chi eq.not chi_0$, there exists $y in G$ such that $chi(y) eq.not 1$.
Then, we have
$ EE_(x in G) chi(x) = EE_(x in G) chi(x+y) = chi(y) dot EE_(x in G) chi(x). $
Since $chi(y) eq.not 1$, we conclude that $EE_(x in G) chi(x) = 0$.
]
You can find a more detailed example in example.typ
.
There is a slight problem with equations, where the subsequent paragraph is not indented.
To amend this, you can add a $zws$ #v(-15pt)
after it.
Moreover, operators and greek letters are by default italicized inside theorems, lemmas and propositions.
To fix that (in this example, the
#let log = $upright(log)$
to force it to look like