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Path: ...!weretis.net!feeder8.news.weretis.net!news.szaf.org!news.karotte.org!news.space.net!news.muc.de!.POSTED.news.muc.de!not-for-mail From: Alan Mackenzie <acm@muc.de> Newsgroups: sci.math Subject: Re: How many different unit fractions are lessorequal than all unit fractions? Date: Sat, 5 Oct 2024 13:57:30 -0000 (UTC) Organization: muc.de e.V. Message-ID: <vdrgka$sn2$3@news.muc.de> References: <vb4rde$22fb4$2@solani.org> <vdo8ke$586f$3@dont-email.me> <vdodmu$5sti$4@dont-email.me> <vdoeft$6biq$1@dont-email.me> <vdof0j$5suf$3@dont-email.me> <vdogjq$6l4c$1@dont-email.me> <vdpbuv$alvo$1@dont-email.me> <8c94a117d7ddaba3e7858116dc5bc7c66a46c405@i2pn2.org> <vdqttc$mnhd$1@dont-email.me> <vdr1g3$n3li$6@dont-email.me> <8ce3fac3a0c92d85c72fec966d424548baebe5af@i2pn2.org> <vdrd5q$sn2$2@news.muc.de> <55cbb075e2f793e3c52f55af73c82c61d2ce8d44@i2pn2.org> Injection-Date: Sat, 5 Oct 2024 13:57:30 -0000 (UTC) Injection-Info: news.muc.de; posting-host="news.muc.de:2001:608:1000::2"; logging-data="29410"; mail-complaints-to="news-admin@muc.de" User-Agent: tin/2.6.3-20231224 ("Banff") (FreeBSD/14.1-RELEASE-p3 (amd64)) Bytes: 2215 Lines: 29 Richard Damon <richard@damon-family.org> wrote: > On 10/5/24 8:58 AM, Alan Mackenzie wrote: >> Richard Damon <richard@damon-family.org> wrote: >> [ .... ] >>> But actual infinity doesn't exist. >> What does it mean for a mathematical concept not to exist? > That it doesn't create a usable (non-contradictory) logical system. Yes! At least, sort of. My understanding of "doesn't exist" is either the concept is not (yet?) developed mathematically, or it leads to contradictions. WM's "dark numbers" certainly fall into the first category, and possibly the second, too. I first came across the terms "potential infinity" and "actual infinity" on this newsgroup, not in my degree course a few decades ago. I'm not convinced there is any mathematically valid distinction between them. If there were, I would have heard of it back then. Does "actual infinity" create a logical system? If so, what is unusable or contradictory about that system? [ .... ] -- Alan Mackenzie (Nuremberg, Germany).