I think this is all you need for that particular layout though

\documentclass[10pt,a4paper,norsk]{book}
\usepackage{graphicx} % use [demo] to temporarily remove all figures
\usepackage{%
fixltx2e,%
lmodern,%
fix-cm} % Better typhography

\usepackage[activate={true,nocompatibility},final,tracking=true,kerning=true,spacing=true,factor=1100,stretch=10,shrink=10]{microtype} \LoadMicrotypeFile{bch}
\microtypecontext{spacing=nonfrench}
\usepackage{tgheros} \usepackage{charter}

@BalarkaSen So, in order to prove that $\epsilon_p$ is a ring homomorphismcould we do it like that? Or have I done something wrong?

Let $a,b \in \mathbb{Z}$. Then:

$\epsilon_p(a+b)=((a+b) \mod {p},(a+b) \mod {p^2}, (a+b) \mod {p^3}, \dots )=(a \mod{p}+b \mod{p}, a \mod{p^2}+b \mod{p^2}, a \mod{p^3}+b \mod{p^3}, \dots)=\epsilon_p(a)+ \epsilon_p(b)$


$\epsilon_p(ab)=(ab \mod {p},ab \mod {p^2}, ab \mod {p^3}, \dots )=(a \mod{p} \cdot b \mod{p}, a \mod{p^2} \cdot b \mod{p^2}, a \mod{p^3} \cdot b \mod{p^3}, \dots)=\epsilon_p(a) \cdot \epsilon_p(b)$