Wikipedia:Articles for deletion/Union of two regular languages


 * The following discussion is an archived debate of the proposed deletion of the article below. Please do not modify it. Subsequent comments should be made on the appropriate discussion page (such as the article's talk page or in a deletion review).  No further edits should be made to this page.

The result was delete. If users believe a redirect is merited, they are free to create one. ✗ plicit  00:18, 18 November 2021 (UTC)

Union of two regular languages

 * – ( View AfD View log )

Near-orphaned information more appropriately explained at Thompson's construction and Nondeterministic finite automaton Caleb Stanford (talk) 12:16, 10 November 2021 (UTC)

See here for some info on the page's origin. The page is a copied proof from a textbook and the information in the proof is explained better elsewhere.
 * Note: This discussion has been included in the list of Mathematics-related deletion discussions. XOR&#39;easter (talk) 14:22, 10 November 2021 (UTC)


 * Delete for the reasons above (not sure whether I'm supposed to comment on my own proposed AfD). Caleb Stanford (talk) 15:52, 10 November 2021 (UTC)
 * Nominating the article counts as voicing your opinion that it ought to be deleted, so you don't have to say "delete" again. XOR&#39;easter (talk) 16:15, 10 November 2021 (UTC)
 * Logging delete agreement from Jochen Burghardt here: "An additional argument is that the proof has several flaws. I tagged those I found in 2014, but no attempts were made to fix (or deny) them." Caleb Stanford (talk) 15:55, 10 November 2021 (UTC)
 * Delete Lengthy blob of opaque, partially undefined notations without any indication of why a step-by-step proof is necessary. The claim being proved is unsurprising (at least one textbook introduces it with It is clear that... ). I don't see why an article on this is needed; the property is the kind of thing we could state without proof, or state and then outline a proof in words. XOR&#39;easter (talk) 16:36, 10 November 2021 (UTC)
 * Delete and redirect to Alternation (formal language theory) (without merging). This is standard textbook material, and the alternation operation is notable and encyclopedic. But although the NFA-based proof of closure given here works only for alternation, the DFA-product-based proof is more general and works for all other Boolean combinations. In any case the proof itself is not independently notable, and I don't think this one closure property is so distinct from the others to stand alone as an article. —David Eppstein (talk) 08:42, 11 November 2021 (UTC)
 * Comment: To me "alternation" in formal language theory means alternating existentials and universals (a la Chandra & Stockmeyer) (also happy with the Boolean combination definition), I've never seen the usage of it as another word for "union", but would agree with the redirect if the target page is changed to be something more interesting. Caleb Stanford (talk) 14:20, 11 November 2021 (UTC)
 * The target page is exactly on unions of formal languages. What does "more interesting" have to do with it? —David Eppstein (talk) 16:47, 11 November 2021 (UTC)
 * I am suggesting that the target page should either be called Union (formal language theory), be rewritten to discuss alternation in the sense of alternating automata and alternating Turing machines, or deleted. Using the word "alternation" for a union is at best confusing. Caleb Stanford (talk) 17:00, 11 November 2021 (UTC)
 * It is the technical word used within this subject area for that meaning. Your confusion is irrelevant. Your confusion between automata theory and formal language theory is also irrelevant (both the target and the nominated article are on formal languages, not automata, and alternating Turing machines do something quite different despite the similar name). And renaming other articles to words different from the ones used in their fields to describe their topic should not be relevant for whether we redirect one article on a topic to another article on the same topic. —David Eppstein (talk) 20:20, 11 November 2021 (UTC)
 * With all due respect, I am an expert in formal language and automata theory and have never heard the word used this way. Nor do the references include any formal language theory paper with this usage, but there are dozens of formal language theory papers where alternation means quantifier alternation. If it is indeed true that some experts use this terminology, then the fact that they insist on having another word for "union" is a bit baffling to me. Caleb Stanford (talk) 20:33, 11 November 2021 (UTC)
 * If you think of a language as a set, it is the union. If you think of a language as being recognized by a pattern described by an expression, you need a name for the operation used in those expressions, which is not a union (patterns are not sets). The following all use "alternation" in the sense of the union of formal languages: "LR-parsing of extended context free grammars", Madsen & Kristensen 1976, 10.1007/BF00265221; "A compact function for regular expression pattern matching", Richards 1979, 10.1002/spe.4380090703; "On String Pattern Matching: A New Model with a Polynomial Time Algorithm", Liu, 1981; 10.1137/0210010; "Finding Regular Simple Paths in Graph Databases", Mendelzon & Wood 1995, 10.1137/S009753979122370X; "Regular expression types for XML", Hosoya et al 2005, 10.1145/1053468.1053470; "String generation for testing regular expressions", Zheng et al 2020, 10.1093/comjnl/bxy137; and no doubt many others. —David Eppstein (talk) 20:46, 11 November 2021 (UTC)
 * Thanks for substantiating the claim --- I agree then, that this terminology is sometimes used. It is not Wikipedia's job to arbitrate which terminology should be standard, so the article name should stand as it is with appropriate clarification. I hope my tone did not come across as antagonistic, that was not my intention. I would not mind redirecting there. Thanks for the discussion. Caleb Stanford (talk) 21:01, 11 November 2021 (UTC)


 * The above discussion is preserved as an archive of the debate. Please do not modify it. Subsequent comments should be made on the appropriate discussion page (such as the article's talk page or in a deletion review). No further edits should be made to this page.