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Fix a couple of errata, a couple of clarifications, and fix a bunch of
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mispellings and other such issues.
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jirilebl committed Jul 9, 2022
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59 changes: 31 additions & 28 deletions ca.tex
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Expand Up @@ -2475,7 +2475,7 @@ \subsection{Elementary calculus}

\begin{exercise}
Prove the last two items of \propref{prop:powerrule}:
Polynonomials $P(z)$ are holomorphic on $\C$ (and compute their derivative),
Polynomials $P(z)$ are holomorphic on $\C$ (and compute their derivative),
and rational functions
$\frac{P(z)}{Q(z)}$ are holomorphic on the set where $Q$ is nonzero.
\end{exercise}
Expand Down Expand Up @@ -5550,7 +5550,7 @@ \subsection{Cauchy's formula in a disc}
\end{exercise}

\begin{exercise} \label{exercise:strongerCIFdisc}
Strenghten the theorem: Show that the conclusion holds if
Strengthen the theorem: Show that the conclusion holds if
we only assume that $f \colon \overline{\Delta_r(p)} \to \C$
is continuous and $f$ is holomorphic on $\Delta_r(p)$.
\end{exercise}
Expand Down Expand Up @@ -8605,7 +8605,7 @@ \section{Laurent series}

Finally, we can differentiate and antidifferentiate
formally, in the same way as we did it for power series. The one minor
hickup is that we cannot antidifferentiate the $c_{-1}{(z-p)}^{-1}$ term.
hiccup is that we cannot antidifferentiate the $c_{-1}{(z-p)}^{-1}$ term.
The proof is left as an exercise.

\begin{prop} \label{prop:diffantidifflaurent}
Expand Down Expand Up @@ -10850,7 +10850,7 @@ \section{Residue theorem}
f(z) \, dz .
\end{equation*}
That is, going around a circle in reverse is going around infinity rather
than the center (if what we are \myquote{going around} is defined to be whaterver
than the center (if what we are \myquote{going around} is defined to be whatever
is on our left).
\item
If $f$ is holomorphic on $\C$ except for finitely many isolated
Expand Down Expand Up @@ -14004,7 +14004,7 @@ \subsection{The Dirichlet problem in a disc and the Poisson kernel}

We remark that in the proof we used the topology on $\overline{\D}$
given by the polar coordinates, and we estimated the coordinates separately.
Polar coordinates give a nice local homemorphism
Polar coordinates give a nice local homeomorphism
(a continuous bijective map with a continuous inverse) outside of
the origin, which is sufficient for us as we only worried about points
on or near the boundary of $\D$. The reader that is still unconvinced
Expand Down Expand Up @@ -14708,7 +14708,7 @@ \subsection{Harnack's principle}
\begin{exparts}
\item
If $f_n(p) \to +\infty$, then $\{ f_n \}$ converges to $+\infty$ uniformly on
compact subets.
compact subsets.
\item
If $f \colon U \to \R$ is harmonic, $f_n(z) \leq f(z)$ for all $z \in U$,
and $f_n(p) \to f(p)$, then $\{ f_n \}$ converges to $f$ uniformly on
Expand Down Expand Up @@ -15159,7 +15159,7 @@ \subsection{Basic properties}

\begin{exercise}
Prove that if $f \colon U \to \R$ is upper-semicontinuous and $-f$ is also
upper-semicontinuous (that is $f$ is also lower-semicontinuous), then $f$
upper-semicontinuous (that is, $f$ is also lower-semicontinuous), then $f$
is continuous.
\end{exercise}
\end{exbox}
Expand All @@ -15180,7 +15180,7 @@ \subsection{Basic properties}
\end{exercise}
\end{exbox}

Suharmonic functions are also classified by a mean-value-like property,
Subharmonic functions are also classified by a mean-value-like property,
although it is an inequality rather than an equality. There is a subtle
issue of integrability. For an upper-semicontinuous function
the integral in the theorem need not exist as a Riemann integral.
Expand Down Expand Up @@ -15349,7 +15349,10 @@ \subsection{Basic properties}
\begin{thm}[Maximum principle]
\index{maximum principle!subharmonic functions}
Suppose $U \subset \C$ is a domain and $f \colon U \to \R \cup \{ -\infty \}$
is subharmonic. If $f$ attains a maximum in $U$, then $f$ is constant.
is subharmonic. If $f$ attains a maximum\footnote{%
We do mean the global maximum; if the maximum is local, one only
obtains constancy nearby.}
in $U$, then $f$ is constant.
\end{thm}

\begin{proof}
Expand Down Expand Up @@ -15405,7 +15408,7 @@ \subsection{Basic properties}
\begin{exercise}
Prove the minimum principle for superharmonic functions ($f$ is
superharmonic if $-f$ is subharmonic). That is, if a superharmonic function
defined on a domain $U$ achieves a local minimum inside $U$, then it is
defined on a domain $U$ achieves a minimum inside $U$, then it is
constant.
\end{exercise}
\end{exbox}
Expand Down Expand Up @@ -15522,7 +15525,7 @@ \subsection{Basic properties}
\item
If $\{ p_n \}$ is dense in $U$, show that $f$
is nowhere continuous.
Hint: Prove $f^{-1}(-\infty)$ is a small (but dense) set.
Hint: Prove $f^{-1}(-\infty)$ is a small but dense set.
Hint \#2: Integrate the partial sums, and use polar coordinates.
\end{exparts}
\end{exercise}
Expand Down Expand Up @@ -15630,7 +15633,7 @@ \subsection{Applications, Rad\'o's theorem}
through this technique, which is called the \emph{\myindex{Perron method}}.
Clearly, that technique would work far better than the Poisson kernel for
more complicated domains. For instance, the Poisson kernel can be computed
for simply connected domains provided we know the Riemann map. However,
for simply connected domains with nice boundary provided we know the Riemann map. However,
the kernel is difficult to compute in general, and it requires a very nice
boundary to be able to integrate. The Perron method works much more
generally provided you can construct enough subharmonic functions (which
Expand Down Expand Up @@ -16427,7 +16430,7 @@ \subsection{Factorization of sine}
\begin{equation*}
F(z) = \prod_{n=1}^\infty f_n(z)
\end{equation*}
for holomorphic functions $f_n \colon U \to \C$ converges uniformly
for holomorphic functions $f_n \colon U \to \C$ converging uniformly
on compact subsets of $U$. Prove that
\begin{equation*}
\frac{F'(z)}{F(z)} = \sum_{n=1}^\infty \frac{f_n'(z)}{f_n(z)} ,
Expand Down Expand Up @@ -16597,8 +16600,8 @@ \subsection{The product theorem in any open set}

\begin{exercise}
Given a domain $U \subset \C$ and a sequence $\{ a_n \}$ of distinct points in $U$
with no limit points in $U$. Find a holomorphic function on
$U \setminus \{ a_n \}$, that has essential
with no limit points in $U$, find a holomorphic function on
$U \setminus \{ a_n : n \in \N \}$ that has essential
singularities at $\{ a_n \}$.
\end{exercise}

Expand Down Expand Up @@ -16846,7 +16849,7 @@ \section{Runge's theorem}
In some parts of the proof below, to simplify the verbiage, we will say that
functions of a certain type (uniformly) approximate $f$ on $K$
if for every $\epsilon > 0$ there exists a function $g$
of a the given type such that
of the given type such that
$\sabs{f(z)-g(z)} < \epsilon$ on $K$. We leave the following statement as
a simple exercise in chasing those epsilons.

Expand Down Expand Up @@ -17144,14 +17147,14 @@ \section{Runge's theorem}
there is a sequence of holomorphic $f_n \colon W \to \C$ such that converge
uniformly on compact subsets of $U$ to $f$.
\item
Suppose there is at least one $p \in \partial U$ such that
Find a counterexample $U$ and $f$ to the conclusion of part a) where
there is at least one $p \in \partial U$ such that
$\Delta_\epsilon(p) \setminus \widebar{U}$ is empty for some $\epsilon > 0$.
Find a counterexample $U$ and $f$ to the conclusion of part a).
\item
Suppose there is at least one $p \in \partial U$ such that
Find a counterexample $U$ and $f$ to the conclusion of part a) where
there is at least one $p \in \partial U$ such that
$\Delta_\epsilon(p) \setminus \widebar{U}$ is nonempty but disconnected for
every $\epsilon > 0$.
Find a counterexample $U$ and $f$ to the conclusion of part a).
\end{exparts}
\end{exercise}
\end{exbox}
Expand Down Expand Up @@ -17326,7 +17329,7 @@ \section{Polynomial hull and simply-connectedness}

\begin{exbox}
\begin{exercise}
Suppose that $U \subset \C$ is a polynomially convex domain such that for each
Suppose $U \subset \C$ is a polynomially convex domain such that for each
$p \in \C$ there exists an $M$ such that $\partial \Delta_M(p) \subset U$.
Prove that $U = \C$.
\end{exercise}
Expand All @@ -17343,7 +17346,7 @@ \section{Polynomial hull and simply-connectedness}

\begin{exercise}
Let $U \subset \C$ be a domain. Prove that $U$
is simply coonnected if and only if there exists a sequence $K_n$
is simply connected if and only if there exists a sequence $K_n$
of compact subsets of $U$ such that $K_n \subset K^\circ_{n+1}$,
$\bigcup K_n = U$, and such that $\widehat{K_n} = K_n$.
\end{exercise}
Expand Down Expand Up @@ -17537,7 +17540,7 @@ \section{Mittag-Leffler}
$p \in U$, and
$P(z) = \sum_{n=1}^{k} \frac{c_n}{{(z-p)}^n}$.
Suppose
$K \subset U \setminus \{ p \}$ such that $p$ is in the unbounded
$K \subset U \setminus \{ p \}$ is compact such that $p$ is in the unbounded
component of $\C \setminus K$. Show that for every $\epsilon > 0$,
there exists a function $g$ holomorphic in $U \setminus \{ p \}$
with a pole at $p$ and principal part $P$ at $p$ and such that
Expand All @@ -17553,7 +17556,7 @@ \section{Mittag-Leffler}

\begin{exercise}
Suppose that instead of principal parts of poles, $P_p(z)$ are principal
parts of essential singularities, which converge in $\C \setminus \{ p \}$.
parts of essential singularities that converge in $\C \setminus \{ p \}$.
Prove the Mittag-Leffler with this setup.
\end{exercise}

Expand Down Expand Up @@ -17844,8 +17847,8 @@ \section{Schwarz reflection principle}
$\widebar{U}$. (The hard part is continuity at $z=0$.)
\item
Show that $f$ does not extend holomorphically through the
origin. That is, for any open neighborhood $V$ of $0$ there
exists no holomorphic
origin. That is, for no open neighborhood $V$ of $0$ does there
exist a holomorphic
$\varphi \colon V \to \C$ such that $\varphi = f$ on $U \cap V$.
\item
Show that $f$ extends as a
Expand Down Expand Up @@ -18149,7 +18152,7 @@ \subsection{Unrestricted continuation}
\begin{exbox}
\begin{exercise}
Let $U \subset \C$ be a domain, $W \subset U$ a connected open subset,
$p \in W$ and $f \colon U \to \C$ holomorphic. Prove that the restriction
$p \in W$, and $f \colon U \to \C$ holomorphic. Prove that the restriction
$f|_W$ allows unrestricted continuation to $U$ with $p$ as a starting point.
\end{exercise}

Expand Down Expand Up @@ -19547,7 +19550,7 @@ \subsection{Closure and boundary}
\end{proof}

The boundary is the set of points that are close to both the set and its
complement. See \figureref{fig:msboundary} for the a diagram
complement. See \figureref{fig:msboundary} for a diagram
of the next proposition.

\begin{prop}
Expand Down
4 changes: 4 additions & 0 deletions changes-draft.html
Original file line number Diff line number Diff line change
Expand Up @@ -35,4 +35,8 @@
<li>In Exercise 6.2.2, emphasize that \(U \subset {\mathbb{C}},\) as the two
notions are not the same in an arbitrary metric space.
<li>Reword part a) of 6.2.6 to be more explicit.
<li>In Theorem 7.4.5 (maximum principle for subharmonic functions),
add a footnote to draw attention to the maximum now being
a global one.
<li>Reword parts b and c of Exercise 9.2.7 to be more logical.
<li>Add some more hyperlinks.

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