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Semigroups Admitting Relative Inverses
A. H. Clifford · Annals of Mathematics · 1941 · 226 citations
Mario Petrich, A. H. Clifford · Semigroup Forum · 1978 · 146 citations
The structure of idempotent semigroups. I
Naoki Kimura · Pacific Journal of Mathematics · 1958 · 118 citations · Full text
David McLean · American Mathematical Monthly · 1954 · 110 citations
Jonathan Leech · Algebra Universalis · 1989 · 84 citations