An example of a semigroup where a D-class is a subsemigroup but not bisimple.
Iyengar, H.R.K.
Semigroup forum, Tome 1 (1970), p. 182-183 / Harvested from Göttinger Digitalisierungszentrum
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Publié le : 1970-01-01
EUDML-ID : urn:eudml:doc:133789 
@article{GDZPPN001247131,
     title = {An example of a semigroup where a D-class is a subsemigroup but not bisimple.},
     journal = {Semigroup forum},
     volume = {1},
     year = {1970},
     pages = {182-183},
     zbl = {0207.03103},
     url = {http://dml.mathdoc.fr/item/GDZPPN001247131}
}

Iyengar, H.R.K. An example of a semigroup where a D-class is a subsemigroup but not bisimple.. Semigroup forum, Tome 1 (1970) pp. 182-183. http://gdmltest.u-ga.fr/item/GDZPPN001247131/