Howie 1995, p.54(en) John M. Howie, Fundamentals of Semigroup Theory, Oxford, Oxford University Press, coll.«London Mathematical Society Monographs. New Series» (no12), , x+351 (ISBN0-19-851194-9, MR1455373)
Howie 1995, Theorem 5.1.1 (en) John M. Howie, Fundamentals of Semigroup Theory, Oxford, Oxford University Press, coll.«London Mathematical Society Monographs. New Series» (no12), , x+351 (ISBN0-19-851194-9, MR1455373)
Howie 1995, Lemma 2.4.4 (en) John M. Howie, Fundamentals of Semigroup Theory, Oxford, Oxford University Press, coll.«London Mathematical Society Monographs. New Series» (no12), , x+351 (ISBN0-19-851194-9, MR1455373)
Howie 1995, p.55(en) John M. Howie, Fundamentals of Semigroup Theory, Oxford, Oxford University Press, coll.«London Mathematical Society Monographs. New Series» (no12), , x+351 (ISBN0-19-851194-9, MR1455373)
Howie 1995, Proposition 2.4.1 (en) John M. Howie, Fundamentals of Semigroup Theory, Oxford, Oxford University Press, coll.«London Mathematical Society Monographs. New Series» (no12), , x+351 (ISBN0-19-851194-9, MR1455373)
Howie 1995, Chap. 6 et Section 2.4 (en) John M. Howie, Fundamentals of Semigroup Theory, Oxford, Oxford University Press, coll.«London Mathematical Society Monographs. New Series» (no12), , x+351 (ISBN0-19-851194-9, MR1455373)
Howie 1995, p.222(en) John M. Howie, Fundamentals of Semigroup Theory, Oxford, Oxford University Press, coll.«London Mathematical Society Monographs. New Series» (no12), , x+351 (ISBN0-19-851194-9, MR1455373)
Kilp, Knauer et Mikhalev 2000, p.33(en) Mati Kilp, Ulrich Knauer et Alexander V. Mikhalev, Monoids, Acts and Categories: with Applications to Wreath Products and Graphs, Walter de Gruyter, coll.«De Gruyter Expositions in Mathematics» (no29), , xviii+529 (ISBN978-3-11-015248-7, lire en ligne)
Bien au contraire: on peut prouver ((en) «a characterization of groups», sur PlanetMath) qu'un demi-groupe où tout élément possède un pseudo-inverse unique est en fait un groupe.