## Section4An Interesting Corollary

###### ObjectivesFundamental Structures

This is an <objectives> element you are reading, and this is its introduction. This early section has really grown and tries to accomplish many things. Not all of them are listed here.

1. Display various “blocks”, fundamental units of the flow.
2. More.
3. Evermore.

This concludes the (incomplete) objectives for this section, so now we can carry-on as before.

This is a cross-reference to one of the objectives above, forced to use the type-global form of the text. It should describe the objective as belonging to the section (rather than the objectives), since objectives are one-per-subdivision and are numbered based upon the containing division: Objective 1 of Section 4. For comparison this is the (forced) type-global cross-reference: Objective 4.1.

The Fundamental Theorem comes in two flavors, where usually one is a corollary of the other.

### Subsection4.1Second Version of FTC

We simply take the indicated derivative, applying Theorem 2.1 at (4.2)

\begin{align} \frac{d}{dx}\definiteintegral{a}{x}{f(t)}{t}&=\frac{d}{dx}\left(F(x)-F(a)\right)\label{equation-use-FTC}\tag{4.2}\\ &=\frac{d}{dx}F(x)-\frac{d}{dx}F(a)\notag\\ &=f(x)-0 = f(x)\text{.}\label{equation-conclude}\tag{4.3} \end{align}

You can have multiple proofs, and they can have titles which replace the word “Proof” as a heading. Here we just exercise displayed math with no automatic numbering, and an elective number on the middle equation.

\begin{align} \frac{d}{dx}\definiteintegral{a}{x}{f(t)}{t}&=\frac{d}{dx}\left(F(x)-F(a)\right)\notag\\ &=\frac{d}{dx}F(x)-\frac{d}{dx}F(a)\tag{4.4}\\ &=f(x)-0 = f(x)\notag \end{align}

The alternative version of the Fundamental Theorem (FTC) in (4.1) is a compact way to express the result.

For testing purposes, there is a simple bare Sage Cell here.

So if we define a function with its variable employed as a limit of integration, like so

\begin{equation*} K(z)=\definiteintegral{345}{z}{x^4\sin(x^2)}{x} \end{equation*}

then we get the derivative of that function so easily it seems like a mystery,

\begin{equation*} \frac{d}{dz}K(z)=z^4\sin(z^2)\text{.} \end{equation*}

That's it.

For testing purposes, there is a simple Sage Cell here, buried inside an example that should be a knowl (embedded in the page).

We cross-reference the example just prior, Example 4.2, to test the simple Sage cell that will now be part of a cross-reference knowl (an external file).

Our purpose here is to show how you can structure a proof with cases, such as an equivalence structured with the arrows typically used to demonstrate the two “directions” involved in the proof, by using the direction attribute on a case element.

###### (⇒)

Nulla non lectus suscipit, bibendum leo quis, dignissim justo. In urna turpis, tincidunt id elementum id, faucibus ac tellus.

###### (⇐)

Quisque auctor ligula turpis, ut aliquam urna consectetur hendrerit. Aenean porta dolor et justo facilisis feugiat in sed sapien. Nullam porta ex et commodo semper.

###### Case 3b: The inductive step.

A case may also have a title, whose formatting and structure is entirely up to the author. This then becomes the text of a cross-reference, as well.

###### (⇒) Necessity.

If you like, you can have both indications.

###### Case.

No direction, no title, then just a generic title.

We test here that punctuation at the end of the title of a proof is handled correctly.

### Subsection4.2A Pedagogical Note about Subsection 4.1

#### Subsubsection4.2.1Symbolic and Numerical Integrals

The Fundamental Theorem explains why we use the same notation for a definite integral, which is a numerical calculation, 1 Which I think sometimes students lose sight of. and an antiderivative, which is a symbolic expression.

Write a short paragraph which compares, and contrasts, the definite and indefinite integral. This is an exercise which sits in the midst of the narrative, so is formatted more like an example or a remark. It can have a hint and a solution, but this one does not. It can have a title, which this one does.

Hint

Start writing!

#### Subsubsection4.2.2

This subsubsection has a title in the source, but it is empty. That's OK, but not advisable since titles get used lots of places (such as page headers and the table of contents).

Using an “integral sign” for an antiderivative (aka indefinite integral) would seem to make the Fundamental Theorem a fait accompli. So I would suggest not conflating the notation for two very different things until the Fundamental Theorem exposes them as being highly related.

This is an example of an example with a bit more structure. Specifically, the example has a title, as usual, but then has a statement, which is separate from the solution. Why did we implement an example in two ways?

Solution

Authors asked for it and it seemed a very natural thing to do, even if we only had an unstructured version for a long time.

Any kind of question can be marked as such with <question>. Or similarly, as a <problem>. They behave identically to examples, such as the one preceding and are numbered along with theorems, examples. etc.

Solution 1

You can have a solution. Or several, even if you don't ask a question.

Solution 2

See?

There are lots of exercises in this sample article, but mostly they are in special exercise sections. Sometimes you just want to sprinkle some exercises through the narrative. We call these inline exercises, in contrast to divisional exercises. The inline exercises look a bit more like a theorem or definition, with titles and fully-qualified numbers.

These may also have hints, answers and solutions.

Hint

A good hint.

42.

Solution

What was the question?

Just for testing math in knowls, and also extra whitespace in a <p>.

There are many different blocks you can employ, and they mostly behave the same way. A <project> is very similar to a <question> or <problem>

###### Project4.1Start Exploring PreTeXt

You could grab the minimal.xml file from the examples/minimal directory and experiment with that.

Projects get their own independent numbering scheme, since they may be central to your textbook, workbook, or lab manual. If you process this sample article with --stringparam numbering.projects.level 0 then you will get consecutive numbers from the beginning of your book, starting with 1.

###### Exploration4.2Exploring Explorations

This is an <exploration>. Other similar possibilities are <project>, <activity>, <task>, and <investigation>.

Note that projects, activities, explorations, tasks and investigations share the independent numbering scheme, so it is really only intended you use one of these. If you want a variant of the name (e.g. “Directed Activity”) you can use the <rename> facility (Subsection 26.1).

Solution

This is a “solution” to the exploration. In practice, you might choose to not make this visible for students, but instead include it as part of some guidance you might provide to instructors (e.g. an Instructor's Manual).

This is quite the activity upcoming. This is a prelude authored within the activity element, but visually just prior.

Another variant of these project-like items is to possibly include a <hint> and an <answer> before the <solution>.

Hint

Just a little help.

The result, but no help in getting there.

Solution

Everything to get it all done, in detail.

This was quite the activity just now. This is a postlude authored within the activity element, but visually just after.

###### Note4.9A Note on Remarks

<remark>, <convention>, <note>, <observation> and <warning> are designed to hold very simple contents, with no additional structure (no proofs, no solutions, etc.).

But they do carry a title and a number, can be the target of a cross-reference, and may be optionally knowlized in HTML with the html.knowl.remark processing switch.

The next block is a project, demonstrating the use of the task element to structure its parts. You are reading the prelude now. The project has lots of nonsense words, so we can test spacing the nested items. In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

###### Project4.4A very structured project

This is an over-arching introduction to the whole project. We follow with some tasks. In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

###### (a)

This first task is very simple, just a paragraph. In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

###### (b)

Now three paragraphs. In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

###### (c)

This second task is further divided by more tasks. This is its introduction. In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

###### (i)

A really simple subtask. In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

A short paragraph, before an answer.

In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

###### (ii)

A subtask with an answer. In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

Right! In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

###### (iii)

Two simple sub-sub-tasks. In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

###### (B)

Second subsubtask. In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

###### (C)

Third subsubtask. In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

In interdum suscipit ullamcorper

In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

The conclusion of the structured subtask. In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

###### (iv)

A simple task as the last subtask. In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

This concludes our structured second task. In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

###### (d)

This third top-level task is intermediate in complexity, you are reading the statement, which is followed by more items. In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

Hint

One hint. In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

First answer. In interdum suscipit ullamcorper.

Second answer. In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

Solution

At last, the solution. In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

This is a conclusion where you could summarize the project. In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

This postlude appears visually outside the project, but is authored within, to make clear its attachment to the project. In interdum suscipit ullamcorper. Morbi sit amet malesuada augue, id vestibulum magna. Nulla blandit dui metus, malesuada mollis sapien ullamcorper sit amet. Nulla at neque nisi. Integer vel porta felis.

Notes or examples related to computation or technology can go in blocks of the same name.

###### Technology4.10Sample Use of Sage

This would be a good place to talk about Sage, including a cell or two.

But you might want to describe how to use some other calculator, or maybe some numerical method.

#### Subsubsection4.2.4Exercises

###### 1

This is an exercise in an “Exercises” subdivision at the level of a subsubsection. There is no question other than if the numbering is appropriate. Here is a self-referential link: Exercise 4.2.4.1.

The subsubsection has no title in the source, so one is provided automatically, and will adjust according to the language of the document.

Solution

This solution will migrate to a list of solutions in the backmatter. We include a sidebyside as a test.

This is a skinny paragraph which should be just 30% of the width.

And another skinny paragraph which should also be just 30% of the width.

A set of reading questions may have an <introduction>, perhaps for preparatory explanation.

If a student has logged in to the HTML version, then they can answer the reading questions directly in the book. Inline math LaTeX can be entered using $...$ or $...$ delimiters, and inline AsciiMath using backticks ... as delimiters. Here are some gratuitous backticks to check that AsciiMath is only active in the answers to reading questions.

###### 1

This is a reading question that you might have a student answer prior to a class session, based on reading part of the book. A quick glance before class can help you tailor class time to the specific needs of your students. The perfect reading question will reveal whether the student has read and understood the material, and will be difficult to answer if they have not. What do you think of that?

###### 2

And a second one, with a cross-reference to the first, as a check on numbering: Reading Question 4.2.5.1. Reading questions are allowed to have answers, but providing answers misses the point of a reading question, and the answer knowl interacts poorly with the mechanism used to allow students to answer directly in the book. Do you think the schema should ban answers to reading questions?

And for symmetry, a <conclusion>.

#### Subsubsection4.2.6Glossary

A glossary may have an <introduction>, perhaps with some explanation.

bar

A part of foobar. See foobar.

foobar

A synonym for the acronym FUBAR.

And for symmetry, a <conclusion>.

#### Subsubsection4.2.7Solutions for This Subsection

This is an introduction, where you might explain that this division of this subsection contains various hints, answers, solutions of inline exercises, divisional exercises, and/or project-like blocks. See the source to see just how this solutions division was built.

#### Subsubsection4.2.4Exercises

And a conclusion to this solutions division, which may not be readily apparent as distinct from the final division's worth of solutions, but since it is not prefixed with a number, it may be different enough.

### Subsection4.3Theorem-Like Environments

There are a variety of pre-defined environments in PreTeXt. All take a title, and must have a statement. Some have proofs (theorems, corollaries, etc.), while some do not have proofs (conjectures, axioms, principles).

More precisely, <theorem>, <corollary>, <lemma>, <algorithm>, <proposition>, <claim>, <fact>, and <identity>, all behave exactly the same, requiring a statement (as a sequence of paragraphs) followed by an optional proof, and may have an optional title. The elements <axiom>, <conjecture>, <principle>, <heuristic>, <hypothesis>, and <assumption> are functionally the same, barring a proof (since they would never have one!). Definitions are an exception, as it is natural to place <notation> within—see the source for Definition 2.2 for an example.

Sage cells share their results on a per-webpage basis, so if you move to a new chapter, section, or subsection that happens to be on another webpage, your Sage computations are gone and you start fresh. But maybe you need some results from elsewhere. As an author, you can make an exact copy of a cell in another location by placing the code in an external file, which is pure text, freed from any need to format for XML processing. So, in particular, there is no need to escape ampersands and angle brackets, nor is there employment of the CDATA mechanism. But the real value is that there is just one version to edit, and any changes will be reflected in both copies. We demonstrate this in the sample book, since it has the xinclude mechanism in place. In the chapter on groups, find the section on Sage and then find the discussion of subgroups, and you will find an example of two identical Sage cells produced from one source file.

### Subsection4.5Hierarchy

##### Structure

This section of this article has subsections and subsubsections. In a book you can have chapters enclosing multiple sections. There is one finer subdivision, it is achieved with the paragraphs element.

It is basically a sequence of paragraphs, where the first one gets an inline title. You are reading the second, and final, paragraph of one right now. It is useful for organizing very short documents, where numbered subdivisions might be overkill.

##### A Second Paragraphs

This is a second consecutive paragraphs element, so should seem related to its title, but distinct from the two paragraphs in the grouping with the title “Structure” immediately prior.

###### Assemblages: Collections and Summaries

An <assemblage> is a collection, or summary, that does not have much structure to it. So you are limited to paragraphs and friends (p, blockquote, pre) and side-by-sides that do not contain captioned items (sidebyside, sbsgroup). The intent is that contents are not numbered, so cannot be cross-referenced individually, and so also do not become knowls. You may place <image>, <tabular>, and <program> inside a <sidebyside>, in addition to other objects that do not have captions. Note that p may by extension contain lists (ol, ul, dl). Despite limited structure, the presentation should draw attention to it, because the contents should be seen as more important in some way. It should be “highlighted” in some manner. If you need to connect the entire assemblage with material elsewhere, you can do that with the usual xref/xml:id mechanism.

What have we seen so far in this (disorganized) sample?

• Theorems, definitions and corollaries. (Section 2)

• Sage cells, including with R. (Section 3)

• Lots of document structure, like introductions and conclusions (next). (Section 4)

A sample table, as a tabular inside a sidebyside with no caption, follows.

 A B C Uno Dos Tres

This is a small assemblage with no title, simply to make sure the surrounding box behaves properly, especially for output.

###### Assemblages containing $\mu \forall \tau \mathbb{H} = \emptyset \kappa$

It is acceptable for an assemblage to contain mathematical content, even in its title.

### Subsection4.6Introductions and Conclusions

###### An Introductory Introduction

Any subdivision may have a sequence of paragraphs within an <introduction> that precedes subsequent further subdivisions. You are reading one now. They are always leaves of the document structure, so are rendered on some pages that reference the following subdivisions.

An introduction or conclusion is an extremely restrictive container with simple presentation. A title is optional (and probably not advisable). Content is meant to be short and unstructured, in particular, nothing that can be numbered is allowed. If this feels too restrictive, then place your content in an initial numbered subdivision and perhaps title it “Introduction”. Or make your entire subdivion unstructured and place whatever you want into it.

This ends this introduction to introductions.

#### Subsubsection4.6.1Test One

An intervening subsubsection just after an introduction.

#### Subsubsection4.6.2Test Two

An intervening subsubsection just before a conclusion.

Entirely analogous to introductions are conclusions. Any subdivision may have a sequence of paragraphs within a <conclusion> that follows previous further subdivisions. You are reading one now. They are always leaves of the document structure, so are rendered on some pages that reference the preceding subdivisions.

This concludes this conclusion (and this subsection and this section).

### Subsection4.7Some Paragraph-Level Markup

Text within a paragraph may be emphasized with <em> or if you want to take it to the next level you can identify the text as an alert with <alert>.

Similarly, within a paragraph, you can identify edits between versions as inserted text that has been added with <insert> or as with <delete>. Note that these identified edits are slightly different than stale text that you want to retain, but which is no longer relevant, which is accomplished with <stale>. The original request for stale text came from an instructor with an online list of student topics for presentations, and as students claimed topics they were marked as no longer available for other students.

If you need a “fill-in blank”, like this, it can be obtained with an empty <fillin> element that defaults to roughly a 10-character width. You can use the <characters> attribute to make the rule longer or shorter, such as a 40-character blank: . The character count is approximate, based on typical character widths within a proportional font carrying English language text. Adjust to suit, or request a language-specific adjustment if it is critical.

Long after we started this mess, we added PreTeXt tags to mark up tags and attributes. The elements are: <tag>, <tage>, <attr>. Examples of how these render are (respectively): <section>, <hash/>, @width. Perhaps this document will make greater use of these tags.

A conclusion here, which we fill with some numbering tests.

This is a cross-reference to one of the outcomes, forced to use the type-global form of the text. It should describe the outcome as belonging to the section (rather than the outcomes), since outcomes are one-per-subdivision and are numbered based upon the containing division: Outcome 2 of Section 4. For comparison this is the (forced) type-global cross-reference: Outcome 4.2.

###### OutcomesFundamental Structures, Revisited

This is a <outcomes> element you are reading, and this is its introduction. This early section has really grown and we have tried to accomplish many things. Not all of them are listed here.

1. Display various “blocks”, fundamental units of the flow.
2. More, and this is what the cross-references above are pointing to.
3. Evermore.

This concludes the (incomplete) outcomes for this section, so now we can carry-on to the next section.