The Wikipedia article for the bicyclic monoid gives three constructions, one of which starts with a free semigroup. It describes the operation for the bicyclic monoid as concatenation, but the remain descriptions are definitely(adsbygoogle = window.adsbygoogle || []).push({}); notconcatenation (e.g. the product of the two generators is the empty string).

My intuition is that they intended to say that it is "something similar to concatenation," but I just wanted to double-check and make sure I'm not missing something here.

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# Bicyclic Monoid: Not Concatenation?

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