Araújo, JoãoKinyon, MichaelMalheiro, António2015-03-242015-03-242013Araújo, João; Kinyon, Michael, Malheiro, António - A characterization of adequate semigroups by forbidden subsemigroups. "Proceedings of the Royal Society of Edinburgh" [Em linha]. ISSN 0370-1646. Vol. 143, nº 6 (2013), p. 1-70370-1646http://hdl.handle.net/10400.2/3803A semigroup is \emph{amiable} if there is exactly one idempotent in each R∗-class and in each L∗-class. A semigroup is \emph{adequate} if it is amiable and if its idempotents commute. We characterize adequate semigroups by showing that they are precisely those amiable semigroups which do not contain isomorphic copies of two particular nonadequate semigroups as subsemigroups.engjournal article10.1017/S030821051100182X