Why Seven Sketches in Compositionality for category theory?#
Alternative pedagogical resources:
Category theory is an old topic and shouldn’t include much original research. You’ll find most of this book’s instructions have directly applicable or equivalent articles on Wikipedia (which is good).
Open source PDF#
The PDF is open source. At the least, this makes it easy to search for content (e.g. latex macros). You could in theory pull only the source of a question out into some other context (perhaps next to your answer, to avoid the split attention effect).
Although there were many small errors (errata, grammar, etc.) in the original PDF, the advantage of open source is that these can not only be expressed to the authors, but fixed. See the latest pipeline in Pipelines · applied-category-theory / seven-sketches · GitLab for a PDF with some of these kinds of errors fixed.
Even if you’re not fixing errors, being able to build the PDF can be useful for other reasons. You may want to change e.g. the formatting slightly so that it fits more nicely on your computer monitors, or remove content that isn’t particularly interesting.
Building the PDF#
The authors seem realtively open/friendly and kindly provided this file via email; see Library20180913.bib · 5462bb5616b48e89c5775a13409204338a695f8e for the original.
Starting a chapter#
Don’t run into the same issue someone else already struggled with; use the errata in Seven-Sketches suggestions. At the start of every chapter, copy the chapter’s comments to a new Google Doc (for an example, see Review “Seven-Sketches suggestions”). As you read errors/suggestions in your copy of the errata, strikethrough entries that you’ve read and documented in this review (Ctrl-Alt-Shift-5 in Google Docs).
For simple issues (e.g. typos) fix the problem in the
tex source of the PDF and submit a patch to applied-category-theory / seven-sketches · GitLab. You don’t want to read these over and over. However, you also don’t want to make major changes that significantly affect e.g. page numbers you may have naturally memorized or affect the map between your commentary and the commentary of others.
For more complicated issues, add a +1 with your name in the original Seven-Sketches suggestions. Then strikethrough the comment in your own copy of the errata and highlight it red (to reflect your classification). Then copy/move the commentary to your own commentary (in this case, these HTML notes). You’ll want a record of all the errors this in book that affected you in your own review. Why? Similar to typos, you don’t want to have to search for them over and over. When you read your old answers and commentary (review your review), you aren’t going to want to go back to the original errata. In my experience, before I started copying errors/commentary to my own commentary, I got confused several times when trying to understand a particular section and only Seven-Sketches suggestions had commentary, not my own. These more complicated issues should more appropriately be fixed in a second edition of the book.
You could also just delete the comments in Review “Seven-Sketches suggestions”, but on the off chance that you want to bring in new errors that others bring up later this allows for it. That is, maintain a monotone map from one Google document to the other that labels errata you’ve addressed as processed.
I’m also effectively maintaining a monotone map from the PDF to these html notes through chapter/section numbering, etc. You really have to take this approach with any read-only material that you need to edit: everything must be an annotation. In this case, neither the original PDF nor Seven-Sketches suggestions are completely read-only, but we don’t want to heavily edit either. You also don’t want to look for annotations in two places (in other reader’s commentary and your own) so you move their commentary to your own. As is the case for many issues in Seven-Sketches suggestions, you may not even want to pull in all other commentary.
Commentary in the errata that didn’t bother you, didn’t seem to be worth copying, or that you didn’t understand and therefore ignored, can be highlighted blue. Commentary that you haven’t decided what to do with can remain black with a strikethrough.
Reading a chapter#
Arrows sometimes appear to be missing in
zathura; see e.g. Equation 1.5 and Example 4.11. The solution is to zoom in more.
Personal interest in category theory#
Category theory is ubiquitous in mathematics; it’s difficult to read mathematical articles on Wikipedia without an understanding of the topic.
Category theory is also fundamental to programming, and in particular to functional programming. See Is Category Theory useful for learning functional programming? - CS SE and Cats | Semigroup.