What have you tried so far? It might be a good idea to look at a couple of small examples (2x2 or 2x3 matrices) just to see what's going on (especially because you don't know if the statement is true, so you might find a counterexample)
I asked online questions about Proposition 2.1.1:
The answer I got is the following:
I have some questions about the answer I got.
When the person answering says:
##1.##
Is the map ##\mathfrak{q}\mapsto \mathfrak{q} A _\mathfrak{p}## from ##A\setminus \mathfrak{p}\to A_\mathfrak{p}##?
But I don't understand what the author meant for the rest of the sentence in mathematical notation:
##2.##
In the next statement where the author says:
How is ##A\to...
The following are taken from the two sources, 1) from this online page and the book An Introduction to Module Theory by: Ibrahim Assem, Flavio U. Coelho.
In the Abelian Categories chapter in the module theory text on page 157, right after presenting IV.2.21 Definition, the authors states
"Image and coimage may or may not exist, but if they do, then they are unique up to isomorphism (because so are kernels and cokernels).
Also in the reference url page above, the authors present two...
When decomposing a representation ##\rho## of a finite group ##G## into irreducible representations, we can find the number of times the representation contains a particular irrep ##\rho_0## through the character inner product
$$
\langle \chi, \chi_0\rangle = \frac{1}{|G|} \sum_{g\in G} \chi(g) \chi_0(g)^*$$
where ##\chi## and ##\chi_0## are the characters of ##\rho## and ##\rho_0##, respectively. Since all group elements in the same conjugacy class have the same characters, this may be...