How to prove that a set G with an associative binary operation * is a group, given that there's a unique right identity element, and every element has a left inverse?
problem 3.17 from Dan Saracino's Abstract Algebra A First Course
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I think this is answered at https://math.stackexchange.com/questions/3163347/is-a-semigroup-with-unique-right-identity-and-left-inverse-a-group – Gerry Myerson Mar 06 '25 at 05:31