Easily Making CheatSheets with Org-mode

Pretty cheat sheets, or “reference cards”, obtainable from Org-mode files. See section #getting-started below to get started making your own cheat sheets!

The listing sheet, as PDF, can be found here, or as a single column portrait, while below is an unruly html rendition.

This reference sheet is built from a CheatSheets with Org-mode system.

• Extra, Local, Setup
• Project Goal
• CheatSheet Examples
• Why Learn & Relearn?
• Getting Started
• What if it’s not good enough?
• What if I want N columns? Or non-landscape? Or multiple formats?
• Colourful Source Blocks
• break
• Basic Equational Support
• Unicode
• Parallel Environment
• break
• Subsection Support
  • A new child tree
  • Another child tree
• Making ~README.org~

Project Goal

Use the elegant & intuitive Org-mode syntax to produce exquisite reference sheets.

• For example, the boxed section headers here are produced from usual Org headers, as in * my section; and one may use org-ref for citations, as in nameref:name

Read Org-mode for beginners for a refresher!

• For more see The Compact Org-mode Guide.

Execute C-c C-e l o or M-x compile to produce a nice looking PDF of your reference sheet.

CheatSheet Examples

Reference sheets created from this project include:

ElispCheatSheet

Quick reference to the core language of Emacs —Editor MACroS.

Islam

Important figures in the faith.

PrologCheatSheet

Program where everything is a relation —i.e., a database table.

CatsCheatSheet

Listing of common theorems in elementary category theory.

LatticesCheatSheet

Reference sheet for definitions and results in Lattice Theory.

OCamlCheatSheet

Basics of OCaml, “the best imperative language”.

CoqCheatSheet

Reference sheet for the Coq language.

GojuRyuCheatSheet

A quick cheat sheet for common terms in Goju Ryu Karate —the hard-soft style of karate.

Why Learn & Relearn?

The world of ideas is not revealed to us in one stroke; we must both permanently and unceasingly recreate it in our consciousness. —Rene Thom

I think org-mode is ideal for computing cheat sheets especially since it allows us to use org-babel tangle to have small minimal working examples that go along with the ideas.

‘Why’, said the Dodo, ‘the best way to explain it is to do it.’ \newline —Alice’s Adventures in Wonderland

A good stock of examples, as large as possible, is indispensable for a thorough understanding of any concept, and when I want to learn something new, I make it my first job to build one. —Paul Halmos

Getting Started

To use this project for your own cheatsheets, just copy-paste the following into, say, the *scratch* buffer then C-x C-e after the final closing parenthesis.

(let ((your-repo "~/example") ;; Alter this location!
      (enable-local-variables :all))
      ;; Look at my “local variables” below; ensure nothing malicious.
      ;; So no need to be queried about loading them.

 ;; Obtain the submodule then make a /copy/ of this cheatsheet.
 (eshell-command (concat
   "  cd " your-repo
   "; git submodule add https://github.com/alhassy/CheatSheet.git"
   "; cp CheatSheet/CheatSheet.org ."
  ))

 ;; Make your cheat sheet refer to the submodule's setup file.
 (find-file-other-window (concat your-repo "/CheatSheet.org"))
 (beginning-of-buffer)
 (re-search-forward "INCLUDE: CheatSheetSetup.org" nil t)
 (replace-match "INCLUDE: CheatSheet/CheatSheetSetup.org")
 (beginning-of-buffer)
)

;; To remove a submodule:
;; git submodule deinit ⟪path_to_submodule⟫ ; git rm ⟪path_to_submodule⟫

For the README.md to be generated as desired, fill in the macros URL and blurb at the top of this org file to point to your repository and provide a description of what the cheatsheet serves to accomplish.

Keep your submodule up to date by running the following command from the parent project —i.e., your project.

git submodule update

Alternatively:

1. Go to the repo where you want to make a cheat sheet.
2. Add this project as a submodule then copy its core to where you’re working:

   git submodule add https://github.com/alhassy/CheatSheet.git
   ; cp CheatSheet/CheatSheet.org .
   ; cp CheatSheet/README.org .
       

3. Open CheatSheet.org and locate #+INCLUDE: CheatSheetSetup.org then rewrite CheatSheetSetup.org to CheatSheet/CheatSheetSetup.org.

What if it’s not good enough?

“The person who thinks of doing something, is usually passed by the person doing it.”

The more that you read, the more things you will know. The more that you learn, the more places you’ll go. —Dr. Seuss

What if I want N columns? Or non-landscape? Or multiple formats?

At the top, say after the #+INCLUDE: CheatSheet/CheatSheetSetup.org line, add the following.

#+LATEX_HEADER: \def\cheatsheetcols{N}
#+LATEX_HEADER: \landscapefalse

For example, having three narrow columns is useful for term-heavy or formula heavy sheets. In contrast, dense sheets may appear less daunting when rendered as single-column in portrait. Sometimes a double-column portrait is more appropriate.

Press C-c C-c on the following incantation to produce a single column portrait of the cheat sheet.

(with-temp-buffer
    (insert
    "#+EXPORT_FILE_NAME: CheatSheet_Portrait.pdf
     #+LATEX_HEADER_EXTRA: \\landscapefalse \\def\\cheatsheetcols{1}
     #+INCLUDE: CheatSheet.org
    ")

    (let ((org-export-use-babel nil))
      (org-mode)
      (org-latex-export-to-pdf)
      )
)

Colourful Source Blocks

Invoke the following with C-c C-c, or better yet place it in your Emacs configuration, to ensure references are picked up and source code highlighting is turned on using the Minted package —which in turn requires the pygmentize system tool.

(setq org-latex-listings 'minted
      org-latex-packages-alist '(("" "minted"))
      org-latex-pdf-process
      '("pdflatex -shell-escape -output-directory %o %f"
        "biber %b"
        "pdflatex -shell-escape -output-directory %o %f"
        "pdflatex -shell-escape -output-directory %o %f"))

For faster pdf generation, consider invoking:

(setq org-latex-pdf-process
      '("pdflatex -interaction nonstopmode -output-directory %o %f"))

By default, Org exports LaTeX using the nonstopmode option, which tries its best to produce a PDF —which ignores typesetting errors altogether, and therefore is not necessarily ideal when using LaTeX.

Basic Equational Support

\eqn{name}{formula} yields a displayed equation with formula left aligned and name right aligned:

\eqn{name}{formula} Moreover, we can refer to such a formula by invoking \ref{name} —e.g., \ref{Functoriality} and \ref{name}. However, if name involves unicode symbols, then this may cause problems.

See the CatsCheatSheet for examples of this kind.

We may also use org-ref style references, as in eqref:name. However, org-ref may warn that no context for the reference is found —that’s okay.

eqref

Parenthesised reference: eqref:name

autoref

Prefix reference with type: autoref:name

nameref

The name of the section that contains this reference: nameref:name

Unicode

I tend to use a lot of unicode and so this project comes with a unicode style file. We may add additional support for unicode characters as follows.

#+LATEX_HEADER: \newunicodechar{⊕}{\ensuremath{\oplus}}

Below we demonstrate that loops implement finite quantifications by showing how the specification of a loop is implemented, unsurprisingly, using a loop.

A finite quantification can be defined axiomatically by the empty-range rule and split-off term rules. Together these form a recursive definition which can be phrased as a loop.

/*@ requires \valid(A+(0..N-1));
  @ assigns \nothing;
  @ ensures \result ≡ fold(A,0,N);
  @*/
𝑻 fold(int N, 𝑻* A) {

    𝑻 total = identity(⊕);

    /*@ loop invariant
             0 ≤ n ≤ N
          ∧  total ≡ fold(A,0,n);
      @ loop assigns n, total;
      @ loop variant N - n;
    */
    for(int n = 0; n != N; n++)
      total = total ⊕ A[n];
    return total;
}

This pseudo-code is reified by giving concrete values for (𝑻, ⊕, identity) such as (int, +, 0) or (bool, ||, false). Any monoid will do.

Parallel Environment

Cheat sheets should not waste space, so the setup provides a parallel LaTeX enviornment that takes an optional parameter indicating how many columns are desired —two by default. Importantly, we use this environment as if it were any normal org-block:

The initial new line is important, otherwise the parallel environment occurs in-line, which may not be the intended behaviour.

The column break is automatic, but as this is sugar for a minipage containing a multicolum we can force a column separation with \columnbreak.

parallelNB produces a side-by-side rendition with ‘N’o ‘B’ar:

Here is an example with four columns:

Here is an example with three columns and ‘n’o ‘b’ar:

Subsection Support

Ideally a cheat sheet is not too hierarchical and so a subsection, as in ** child, is turned into a rule as follows.

A new child tree

Here is the first child’s content.

Another child tree

Here is the sibling’s content.

Making README.org

Evaluate the following source block with C-c C-c to produce a README file.

(with-temp-buffer
    (insert
    "#+EXPORT_FILE_NAME: README.org
     # HTML: <h1> Easily Making CheatSheets with Org-mode </h1>
     #+OPTIONS: toc:nil d:nil
     # Toc is displayed below at a strategic position.

     {{{blurb}}}

     :Hide:
     This project is to contain a listing of common results in X Theory.

     *The repo contains other articles I've written on X Theory;*
     *which may be read in a blog-format at:*
     https://alhassy.github.io/blog/categories/#Xtheory
     :End:

    *The listing sheet, as PDF, can be found
     [[file:CheatSheet.pdf][here]]*,
     or as a [[file:CheatSheet_Portrait.pdf][single column portrait]],
     while below is an unruly html rendition.

     # Markdown links: [title](target)

     This reference sheet is built from a
     [[https://github.com/alhassy/CheatSheet][CheatSheets with Org-mode]]
     system.

     #+TOC: headlines 2
     #+INCLUDE: CheatSheet.org
    ")

    ;; No code execution on export
    ;; ⟪ For a particular block, we use “:eval never-export” ⟫
    ;;
    (let ((org-export-use-babel nil))
      (org-mode)
      ; (org-md-export-to-markdown)
      ; (package-install 'toc-org)
      (toc-org-mode)
      (toc-org-insert-toc)
      ; (delete "TOC" org-export-exclude-tags)
      (pop org-export-exclude-tags)
      (org-org-export-to-org)
      (add-to-list 'org-export-exclude-tags "TOC")
      )
)

Note that the blurb macro is defined by the user, to provide a terse description of the project.

• Think the one-line statement at the top of a github repo page.