Abstract
It is well known that a product $ab$ in a ring may have an inverse without $ba$ being invertible. However, if $ab$ has a quasi-inverse, then so does $ba$. This note provides a (3-line) proof and an explanation.
Citation
P. M. Cohn. "A remark on the quasi-inverse of a product." Illinois J. Math. 47 (1-2) 87 - 88, Spring/Summer 2003. https://doi.org/10.1215/ijm/1258488140
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