Theorem/Lemma/Definition Custom Blocks

[coatless]

I'm trying to provide a way to use theorems/lemmas/definitions.

The main way I see about going about this is via the custom block declaration:

To enable this feature I'm running into a roadblock of not being able to:

1. supply non-body content like a header (e.g. theorem name)
2. autoincrement/number

For 1. it seems as if caption = "Fermat's Last Theorem" could be passed through to the block more options would be possible.

For 2., I'm pretty sure this isn't possible due to the restriction on the \ref tag.

[yihui]

I did think about this when I started this project, but I didn't come up with a simple solution. I'm preparing the CRAN release of bookdown right now, and I'll reconsider this feature in the next version. Basically there are two possible ways on my mind: 1) As you described, use custom blocks (the major drawback is that it is not easy to use all Markdown features in these blocks at the moment; #117); 2) Hack the definition list or example list http://pandoc.org/README.html#definition-lists using some sort of special tokens and restore them to thereoms/lemmas/whatever.

[yihui]

All these environments have been implemented. Please see the documentation at https://bookdown.org/yihui/bookdown/markdown-extensions-by-bookdown.html

[coatless]

Praise be @yihui .

[endri81]

Environment theorem not working for me. When I compile pdf I get:

In get_engine(options$engine) :
  Unknown language engine 'theorem' (must be registered via knit_engines$set()).

and theorem show just the typed text with different font but not at all as in the documentation

[coatless]

After a bit of configuration, the theorem environments do work.

Questions:

1. Do you have the latest bookdown version? devtools::install_github("rstudio/bookdown")
2. Are you building under bookdown::pdf_book?
3. Did you define theorem environments?
   https://github.com/SMAC-Group/TTS/blob/cb0e8f4f46857b88d11bd429d7be4bc3f2944e7c/preamble.tex#L54-L78

[endri81]

Thank you @coatless very much.
I made the changes now everything works fine
Best Regards

[yihui]

2 and 3 are not necessary. Theorems work for HTML/EPUB output as well. You can also leave the preamble empty, and bookdown will define the environments for you. The documentation said:

For the sake of simplicity and consistency, we do not recommend you to do this (define environments in LaTeX).

[coatless]

@yihui

---

I agree that 2 is unnecessary. This was primarily to make sure that the document was not being knitted (if open in a non-bookdown rstudio project). This is a known issue that a few of my collaborators have run into.

---

On 3, I disagree. I'm not sure that theorem has been defined for the pdf_book.

Without defining the theorem and other environments in the premable.tex, I received:

! LaTeX Error: Environment theorem undefined.

I came to this realization after observing the example text, which explicitly loads amsthm:

bookdown/inst/examples/latex/preamble.tex

Lines 92 to 98 in 1254a81

	\usepackage{amsthm}
	\makeatletter
	\def\thm@space@setup{%
	\thm@preskip=8pt plus 2pt minus 4pt
	\thm@postskip=\thm@preskip
	}
	\makeatother

[yihui]

@coatless I'm loading amsthm explicitly only because I wanted to increase the vertical space above the theorems in the bookdown book, which uses the LaTeX class from Chapman & Hall and the spacing above theorems was too tight. This is only for cosmetic purposes. If your book cannot compile without defining the theorem environments, it is either a bookdown bug or there was something wrong in your book, and I'll need a reproducible example. I didn't define the theorem environments in the bookdown book, and it generates the PDF without any problems.

[stevepowell99]

Is there any way to get a list of definitions / theorems etc at the end of the book?

[yihui]

@stevepowell99 Possible, but not very straightforward. Theorems are not different with normal R code chunks, so chunk references will still work: http://yihui.name/knitr/demo/reference/ Basically echo=FALSE to hide a theorem, and echo=TRUE with the same label to show it later. I'm curious why that could be possibly helpful to readers, though. Personally I very much hate figures/tables being placed at the end of a paper (per requirement of some old-fashioned journals), and I also feel it is inconvenient when theorems are not where they are actually used.

[stevepowell99]

sorry, I just meant to place an index of definitions at the end, but to leave the actual definitions where they belong, in the text.

[yihui]

@stevepowell99 If you mean a LaTeX index, please see the section Index in the docs: https://bookdown.org/yihui/bookdown/ If you mean something else, I think it will be better to explain it with an example.

[stevepowell99]

V sorry if I wasn't clear. The short version is this: presumably bookdown, by the end of the book, knows all the definition labels which have been created in the text? So one could just loop / lapply through them and print them all out, aka Index of Definitions. So the user can look to see, aha, where is "bar2" defined, here it is in the Index of Definitions, let's click on it to get to the definition of bar2 in the text.

Long version:
I just meant something like this, (in markdown, not latex)
in text:

A bar1 is defined as a foo.

...

A bar2 is similarly defined as a foobar.

and then, presumably at the end, I can already do this...

##Index of definitions
@ref(def:bar1)
@ref(def:bar2)

... but I have to know all the labels I created in the text and I have to type them. If bookdown knows about all the definition labels I have created, it could make such an index automatically.

[yihui]

@stevepowell99 By the end of the book, you can obtain all labels of definitions via knitr::all_labels(engine == 'definition'). You can certainly create cross-references automatically, but the problem is you only have the labels, so readers can only see definition numbers like X.Y, and there are no names/terms for the definitions. This issue is not impossible to solve. You may post a question on StackOverflow and I may answer it there, since I think other users may benefit from it, too.

[yihui]

@stevepowell99 FYI: finally found some time to type an answer on SO http://stackoverflow.com/q/40735727/559676

[stevepowell99]

Is there any way to change the names Lemma, Theorem etc which are actually printed at the start of each block, e.g. for another language?

[yihui]

@stevepowell99 https://bookdown.org/yihui/bookdown/internationalization.html

[stevepowell99]

thanks - now I can't see how to translate the token (PART) - is this not possible?

[yihui]

@stevepowell99 No. For HTML output, you only get part numbers like I, II, III, IV, ... For LaTeX output, you have to figure it out by yourself how to change the PART name (may be something like \partname).

[endri81]

For LateX output you have to put the code below before the chapter which begins your part:

(PART) Name of part {-}

For example if you have book organized:

Part 1

Chapter 1

Chapter 2

...

Part 2

Chapter 1

Chapter 2

...

So you begin Chapter 1 in Part 1 with

(PART) Name of part 1 {-}

and Chapter 1 in Part 2 with

(PART) Name of part 2 {-}

Like this you get the organization you want

[stevepowell99]

Thanks @endri81 - I don't have chapter numbering so had left off the {-}, and that led to me seeing PART actually printed before the header, which I didn't want, which is why I wanted the translation ... In short: when writing (PART), leave the {-} in place, as instructed in the docs, even if you aren't using chapter numbering.

[fyuniv]

@stevepowell99 https://bookdown.org/yihui/bookdown/internationalization.html

In latex
\begin{proof}[Sketch of proof] will be printed as

Sketch of proof.

In bookdown, it prints at

Proof.(Sketch of proof)

Is it possible the temporarily change the printed name of the proof environment?

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