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Fix up css for the rahr and move changes to site
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jirilebl committed Nov 9, 2021
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108 changes: 1 addition & 107 deletions changes-draft.html
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This file is a draft of the new changes for http://www.jirka.org/ra/changes.html

The theme of this revision is trying to fix all the minor issues and errata I
could find, and improve clarity, but not make any large changes, nor add any
content. Perhaps the biggest change are 3 new exercises. Two are there to
fix an erratum, and one was sort of kind of hidden part of an old exercise.
There are a few new explanatory sentences here and there,
but nothing new beyond that.

<li>Add a very short finite example of cartesian product after
Definition 0.3.10.
<li>Make Definition 0.3.11 (function) a bit easier to read by explicitly
stating that it is the $y$ that is unique.
<li>In Definition 0.3.11 (function), define codomain. It does appear in at
least one place in the book, and it may be good for the sake of being a
reference book.
<li>Example 0.3.32 is a bit too informal and just leaves out 0 and the
negatives, so add that.
<li>Move the argument for why infimum and supremum are unique to right
after Definition 1.1.2 and note why this means that the notation is
well-defined.
<li>In Definition 1.1.1 (ordered set), label "transitivity" and "trichotomy"
<li>Remove the first sentence of the proof of Proposition 1.1.9 and just
give the example before the proof. It is not really part of the "proof" of
the statement itself.
<li>In the proof of Example 1.2.3, the second displayed estimate, the $h$ is
given as an equality, so the last $\leq$ is actually $=$.
Also show explicitly that $s-h &gt; 0$ to fix erratum.
<li>Improve the wording of proof of 1.4.2, also in the same proof the sets
$A$ and $B$ were being defined but we only used $=$ and not $:=$. Also,
change $b_k$ to just be any number in $(a_k,b_{k-1})$, that is simpler and
sufficient.
<li>In Definition 2.1.9, move the "Some authors use the word monotonic." to a
footnote to simplify the definition.
<li>After definition 2.1.9 mention $\{ n \}$ as an example of a monotone
increasing sequence.
<li>Simplify the proof of Proposition 2.1.10. Don't say anything about the
$B$, we never use the bound, just say the set of values is bounded, that is
good enough to compute the supremum.
<li>After Definition 2.1.16, explicitly mention what we mean by a subsequence
by writing $x_{n_1},x_{n_2},x_{n_3},\ldots$.
<li><b>Add Exercise 2.1.23</b>
<li>In Proposition 2.2.11, recast the proof of unboundedness to not be a
contradiction proof. It's the same idea, but it avoids having to explain
why it is a contradiction, and avoids a contradiction proof.
<li>In Example 2.2.14, use $M$ instead of $N$ for consistency.
<li><b>Add Exercise 2.3.20</b>
<li>Before Proposition 2.5.6, make "tail of a series" a defined term and add
it to index.
<li>Rephrase the last argument in the proof of Proposition 2.5.17 to be a
little bit more straightforward.
<li><b>Add useful remark to Exercise 2.5.6.</b>
<li><b>Add remark to Exercise 2.5.16 about starting the series, and that only
tails satisfy the hypotheses, so that students do not forget to check these
technicalities.</b>
<li>Add footnote on $L=\infty$ to proof of Proposition 2.6.1
<li>Add a better introductory sentence to cluster points in 3.1.1.
<li>In Lemma 3.1.7 and Proposition 3.1.17, add $L \in {\mathbb{R}}$ to the
hypotheses, that makes it clearer that it is a given number.
<li><b>Since every semester I get a question about Exercise 3.1.1, add a
parenthetical remark: Yes one must prove the limit is what one claims
it is.</b>
<li><b>In Exercise 3.1.11, change "Then show $f(x) \to L$ as $x \to c$ for some
$L \in {\mathbb{R}}$" to "Then show that the limit of $f(x)$ as $x \to c$ exists."
Perhaps that will make students not start on the wrong path of starting with
some $L$ existing rather than proving that it exists.</b>
<li>When proving the Thomae function (3.2.12) is continuous at irrational
numbers, note that since the limit of $\{ x_n \}$ is $c$, then every
rational number is in the sequence at most finitely many times.
<li>At the end of example 3.2.13, mention that $g$ is in fact continuous on $B$.
<li>After proof of Lemma 3.3.1, add a short paragraph highlighting the use of
Bolzano-Weierstrass, to emphasize the technique. It changes the pagination
of 3.3 a tiny bit (inadvertently getting less jarring page breaks)
<li>Reword slightly the end of the proof of Example 3.4.3 to improve clarity.
<li>Add two lines of text after proof of Theorem 3.4.4 to make a similar
point as for 3.3.1, again changing pagination of the rest of 3.4 very
slightly.
<li><b>The "In other words" of Exercise 4.1.14 is confusingly stated with an
inequality, while the way to prove it is simply with an equality, that was
a cut and paste typo. Of course it is true with an inequality still.</b>
<li><b>In Exercise 4.1.15 (simple L'Hospital's rule) note that the limit of the
quotient of derivatives must exist, no need to "suppose" it, we're assuming
here that the derivatives are continuous and the denominator is never
zero. Also assume that $g(x)\not= 0$ if $x \not= c$. While it can be
proved that $g(x) \not= 0$ in some neighborhood of $c$, that was not
intended in this simple version.</b>
<li><b>Added Exercise 4.1.16 to keep this sort of exercise explicitly. That
is, if $f'(c) > 0$, then show that $f(x)$ is negative a bit before $c$
and positive for a bit after $c$, thus zero only at $x=c$.</b>
<li>Be a little bit more precise in the proof of Lemma 4.2.2 to say that
all the $x$ and the $y$ are still within $\delta$ of $c$.
<li>In the proof of Proposition 4.2.6 (and also 4.2.7) note explicitly
that $[x,y] \subset I$ because $I$ is an interval.
<li><b>In Exercise 4.2.9, add a note that the student needs to prove that
$g(x)$ is not zero for $x \not= c$ so that the left hand side of the
equality makes any sense at all.</b>
<li><b>In Exercise 4.3.2, ask about the $d$th Taylor polynomial, not the
$(d+1)$th, that was a typo. Though of course the exercise is still true
for $d+1$.</b>
<li>In Definition 5.1.6 and proof of Proposition 5.1.7 use $\ell$ instead of
$m$ since $m$ is used all over the place for a minimum of the function.
<li>In proof of 5.3.5, explicitly mention the domain of $F$ for clarity.
<li>In Propositions 7.2.6 and 7.2.8 explicitly mention that the sets are
subsets of $X$.
<li>Throughout get rid of the use of the word "any" where it could be ambiguous.
<li>Fix a couple of uses of "=" where ":=" is more appropriate.
<li>Improve the typesetting of some statements.
<li>Some minor clarifications and tightening of the language a bit throughout
the book.
<li>
7 changes: 1 addition & 6 deletions changes2-draft.html
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This file is a draft of the new changes for http://www.jirka.org/ra/changes2.html

<li>Make line in Figure 9.6 a bit bolder to make it easier to pick out.
<li>In Proposition 10.3.7, use $\ell$ for the number of balls to make it
clear that the number is quite likely different from the number of
rectangles.
<li>Fix a couple of uses of "=" where ":=" is more appropriate.
<li>Some minor clarifications and fixes to style and grammar.
<li>
4 changes: 2 additions & 2 deletions extra.css
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Expand Up @@ -73,6 +73,6 @@ li { display: list-item; }
}
hr.rahr {
border-style: none;
background-color: #666;
height: 1px;
height: 0px;
border-top: thin solid #666;
}

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