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- Path: sparky!uunet!mcsun!uknet!qmw-dcs!arodgers
- From: arodgers@dcs.qmw.ac.uk (Angus H Rodgers)
- Newsgroups: sci.math
- Subject: A word problem
- Message-ID: <1992Dec12.162349.29729@dcs.qmw.ac.uk>
- Date: 12 Dec 92 16:23:49 GMT
- Sender: usenet@dcs.qmw.ac.uk (Usenet News System)
- Organization: Computer Science Dept, QMW, University of London
- Lines: 25
- Nntp-Posting-Host: io.dcs.qmw.ac.uk
-
- Are there any finitely generated infinite semigroups in which
- the idempotent law holds?
-
- The "free idempotent semigroup" (if that's the name for it) on
- 2 generators has 6 elements. I don't know if the f.i.s. on 3
- generators is infinite, but it's certainly quite big.
-
- In trying to prove the infiniteness of the f.i.s. over a given
- alphabet, say {a,b,c}, you can't build arbitrarily long reduced
- words by a haphazard process of pre- or post- multiplication by
- generators, because some reduced words do not occur as substrings
- of any longer ones, e.g.:
-
- abacaba
- abacbabcabacbab
- abcbabcabacabcbabcaba
- abcbacabcbabcacbabcbacabcbabcac
-
- Is there, nevertheless, a recipe or existence proof for arbitarily
- long reduced words?
- --
- Gus Rodgers, Dept. of Computer Science, |
- Queen Mary & Westfield College, Mile End |
- Road, London, England. +44 71 975 5241 |
- E-mail (JANET): arodgers@dcs.qmw.ac.uk | Post in haste, repent at leisure.
-