diff --git a/tex/H113/sylow.tex b/tex/H113/sylow.tex index 5dc9fb20..8e4a14aa 100644 --- a/tex/H113/sylow.tex +++ b/tex/H113/sylow.tex @@ -142,7 +142,7 @@ \subsection{Step 1: Prove that a Sylow $p$-subgroup exists} Here is the proof. \begin{itemize} - \ii Let $G$ act on $X$ by $g \cdot X \defeq \left\{ gx \mid x \in X \right\}$. + \ii Let $G$ act on $X$ by $g \cdot S \defeq \left\{ gs \mid s \in S \right\}$. \ii Take an orbit $\OO$ with size not divisible by $p$. (This is possible because of our deep number theoretic fact. Since $\left\lvert X \right\rvert$ is nonzero mod $p$ and the orbits partition $X$, @@ -159,10 +159,10 @@ \subsection{Step 1: Prove that a Sylow $p$-subgroup exists} \subsection{Step 2: Any two Sylow $p$-subgroups are conjugate} -Let $P$ be a Sylow $p$-subgroup (which exists by the previous step). -We now prove that for any $p$-group $Q$, $Q \subseteq gPg\inv$. -Note that if $Q$ is also a Sylow $p$-subgroup, then $Q = gPg\inv$ for size reasons; -this implies that any two Sylow subgroups are indeed conjugate. +If $P$ is a Sylow $p$-subgroup and $Q$ is a $p$-group, we prove $Q +\subseteq gPg\inv$. Note that if $Q$ is also a Sylow $p$-subgroup, then +$Q = gPg\inv$ for size reasons; this implies that any two Sylow +subgroups are indeed conjugate. \textbf{Let $Q$ act on the set of left cosets of $P$ by left multiplication.} Note that @@ -176,15 +176,14 @@ \subsection{Step 2: Any two Sylow $p$-subgroups are conjugate} \subsection{Step 3: Showing $n_p \equiv 1 \pmod p$} -Let $\mathcal S$ denote the set of all the Sylow $p$-subgroups. -Let $P \in \mathcal S$ be arbitrary. +Let $\mathcal S$ denote the set of all the Sylow $p$-subgroups. By our +first step, there exists some $P \in \mathcal S$. \begin{ques} Why does $\left\lvert \mathcal S \right\rvert$ equal $n_p$? (In other words, are you awake?) \end{ques} -Now we can proceed with the proof. -Let $P$ act on $\mathcal S$ by conjugation. -Then: +Now we can proceed with the proof. Let $P$ act on $\mathcal S$ by +conjugation. Then: \begin{itemize} \ii Because $P$ is a $p$-group, $n_p \pmod p$ is the number of fixed points of this action.