{"id":20792370,"url":"https://github.com/dirkgroot/extended-set","last_synced_at":"2026-05-25T06:02:59.538Z","repository":{"id":80606702,"uuid":"441269797","full_name":"dirkgroot/extended-set","owner":"dirkgroot","description":"Extended sets in Kotlin","archived":false,"fork":false,"pushed_at":"2021-12-24T21:40:42.000Z","size":68,"stargazers_count":0,"open_issues_count":0,"forks_count":0,"subscribers_count":1,"default_branch":"main","last_synced_at":"2025-01-18T10:50:15.784Z","etag":null,"topics":["extended-set-theory","kotlin","tdd","xst"],"latest_commit_sha":null,"homepage":"","language":"Kotlin","has_issues":true,"has_wiki":null,"has_pages":null,"mirror_url":null,"source_name":null,"license":null,"status":null,"scm":"git","pull_requests_enabled":true,"icon_url":"https://github.com/dirkgroot.png","metadata":{"files":{"readme":"README.md","changelog":null,"contributing":null,"funding":null,"license":null,"code_of_conduct":null,"threat_model":null,"audit":null,"citation":null,"codeowners":null,"security":null,"support":null,"governance":null,"roadmap":null,"authors":null,"dei":null,"publiccode":null,"codemeta":null}},"created_at":"2021-12-23T18:52:18.000Z","updated_at":"2021-12-24T21:40:45.000Z","dependencies_parsed_at":null,"dependency_job_id":"2f5ea070-1de6-435c-82b4-e53c57299702","html_url":"https://github.com/dirkgroot/extended-set","commit_stats":null,"previous_names":[],"tags_count":0,"template":false,"template_full_name":null,"repository_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/dirkgroot%2Fextended-set","tags_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/dirkgroot%2Fextended-set/tags","releases_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/dirkgroot%2Fextended-set/releases","manifests_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/dirkgroot%2Fextended-set/manifests","owner_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/owners/dirkgroot","download_url":"https://codeload.github.com/dirkgroot/extended-set/tar.gz/refs/heads/main","host":{"name":"GitHub","url":"https://github.com","kind":"github","repositories_count":243136256,"owners_count":20241989,"icon_url":"https://github.com/github.png","version":null,"created_at":"2022-05-30T11:31:42.601Z","updated_at":"2022-07-04T15:15:14.044Z","host_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub","repositories_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories","repository_names_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repository_names","owners_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/owners"}},"keywords":["extended-set-theory","kotlin","tdd","xst"],"created_at":"2024-11-17T15:50:29.107Z","updated_at":"2025-12-25T06:44:46.356Z","avatar_url":"https://github.com/dirkgroot.png","language":"Kotlin","funding_links":[],"categories":[],"sub_categories":[],"readme":"# Extended sets in Kotlin\n\n## Goal\n\nPractice, learning, having fun.\n\n## Introduction\n\nSince about 1-2 years ago, I'm a somewhat regular reader of Ron Jeffries' blog\n(\u003chttps://ronjeffries.com/\u003e). Recently he started a new series of blogs about extended set theory,\nor XST for short. In this series Ron shares the adventures het has in implementing a set-theoretic\ndata structure, based on XST, in Codea Lua.\n\nI didn't know about XST before Ron started writing about it, but now I know of it's existence, it\nhas me thoroughly intrigued. So much, that I felt the urge to see how extended sets (or XSets for\nshort) could be implemented in a somewhat useful way in Kotlin.\n\n## What is XST?\n\nExtended set theory is a replacement for set theory, invented by Dave Childs, which extends set\ntheory with the concept of scopes. Every element in a set is an element of that set under a certain\nscope.\n\nIn \"classical\" set theory, we write **x ∈ S** to denote that **x** is an element of **S**. In\nextended set theory, we write **x ∈\u003csub\u003es\u003c/sub\u003e S** to denote that **x** is an element of **S**\nunder scope **s**. A \"classical\" set looks like this: **{ Mike, London, 42 }**. An extended version\nof this set could look like this: **{ Mike\u003csup\u003ename\u003c/sup\u003e, London\u003csup\u003ecity\u003c/sup\u003e, 42\u003csup\u003eage\u003c/sup\u003e\n}**.\n\nFrom this simple example, I think it's clear that thanks to the added scope, we could represent any\ndata structure as a set (of sets (of sets (of... well, you get it))).\n\n## More information\n\nInformation about XST is not easy to find online (it doesn't even have it's own Wikipedia page).\nHowever, \u003chttp://xegesis.org\u003e contains a couple of articles and papers about XST. I found\n[this paper](http://xsp.xegesis.org/Xsp-uxr.pdf) quite easy to read and informative.\n","project_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fdirkgroot%2Fextended-set","html_url":"https://awesome.ecosyste.ms/projects/github.com%2Fdirkgroot%2Fextended-set","lists_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fdirkgroot%2Fextended-set/lists"}