# Tim Button’s Open Set Theory now part of the Open Logic Project

Tim Button (University College London) based an entire (open) textbook on set theory on the existing set theory coverage of the Open Logic Project, and agreed to have his changes and additions included in the main repository. The material from his Open Set Theory is now folded into the content directory of the OLP. There is also a new textbook, closely resembling the original Open Set Theory. The PDF of Set Theory: An Open Introduction can be found, like all the others, on builds.openlogicproject.org.

Incorporating Open Set Theory into the OLP structure required a few changes to existing material. The coverage of naive set theory in content/sets-functions-relations is now extended by two additional chapters, but in order to fit with later developments, some of the material in the size-of-sets chapter now comes in two versions. I’ve tried to make these changes as much backwards compatible as possible, but if you are including any of this material in your own remixes, you might see some odd results after updating to the new version. Specifically, there is now a new relations/equivalence-relations section (split off from special-properties), and the long section size-of-sets/enumerability has been split, with new separate sections zig-zag, pairing, and pairing-alt. The last two sections are rewritten.

The other material from Open Set Theory now mainly lives in a new content/set-theory part and a content/history/set-theory chapter. The material has been changed minimally, mainly to conform to spelling and stylistic conventions in the rest of the OLP.

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1. ##### Mini-Heap - Daily Nous

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