@article{GDZPPN001257447,
title = {Idempotent-generated subsemigroups of the symmetric semigroup of degree four: computer investigations.},
journal = {Semigroup forum},
volume = {31},
year = {1985},
pages = {119-122},
zbl = {0565.20047},
url = {http://dml.mathdoc.fr/item/GDZPPN001257447}
}
Todorov, K.; Bijev, B. Idempotent-generated subsemigroups of the symmetric semigroup of degree four: computer investigations.. Semigroup forum, Tome 31 (1985) pp. 119-122. http://gdmltest.u-ga.fr/item/GDZPPN001257447/