Accurate description of the difference between the centralizer and the normalizer of a set $S$ in a group $G$?

Question

I've been reading some responses to the common question "What is the difference between the centralizer and the normalizer" and while I know it would make more sense to see if my understanding of the difference is correct by commenting on one of those post I do not yet have enough points to comment. So here's my understanding of the difference.

Give a group $G$ and a set $S$ in $G$ the centralizer of $S$ in $G$ is all the elements $g \in G$ such that given $y \in S$ we have $gyg^{-1} = y$. Whereas the normalizer of $S$ in $G$ is all the elements $g \in G$ such that for any $x \in S$ we have $gxg^{-1} = z$ for some $z \in S$.

In other words it seems like a centralizer of $S$ in $G$ is the elements of $G$ which commute with all of $S$ and the noramlizer of $S$ in $G$ is all the elements $g$ of $G$ which sends $S$ back to $S$ when an element of $S$ is multiplied on the left by $g$ and on the right by $g^{-1}.$

Is that correct?

Do you have advice on better ways to understand the difference between a normalizer and a centralizer?

Is there a more concise way to describe the difference with words or set notation?

Is there an especially illustrative example to help one see the difference? (I have seen the example of $S_3$ and how $A_3$ is a centralizer but $S_3$ itself is the normalizer.)

Answer 1

Is that correct?

Yes, you're correct.

Do you have advice on better ways to understand the difference between a normalizer and a centralizer?

"The only way to learn mathematics is to do mathematics." Paul R. Halmos.

Practice, basically.

That, and the fact that the normaliser $N_G(S)$ of $S$ in $G$ is the smallest normal subgroup of $G$ containing $S$, whereas the centraliser $C_G(S)$ is the group of elements that commute with all elements of $S$ (and no other elements).

Is there is a more concise way to describe the difference with words or set notation?

Yes: use their definitions that use set building notation. See this other answer to your question, by @CharlesHudgins.

Is there an especially illustrative example to help one see the difference? (I have seen the example of $S_3$ and how $A_3$ is a centralizer but $S_3$ itself is the normalizer.)

What's wrong with the one you have already?

Answer 2

The answer already given is perfect. I just want to offer some alternative notation. One often sees the definitions \begin{align} N_G(S) &= \{g \in G \mid gSg^{-1} = S\} \\ C_G(S) &= \{g \in G \mid \forall s \in S, \ gsg^{-1} = s \} \end{align} In words, $N_G(S)$ is the set of elements of $G$ that fix $S$ under conjugation, and $C_G(S)$ is the set of elements of $G$ that fix each element of $S$ under conjugation.