[1] J. Calais: 
Demi-groupes quasi-inversifs. C.R. de I'Acad. des Sci. Paris 252 (1961), 2357-59. 
MR 0123628 | 
Zbl 0097.01104 
[2] A. H. Clifford, G. B. Preston: 
The Algebraic Theory of Semigroups, Vol. I. 11, Math. Survey 7, Am. Math. Soc., 1961, 1967. 
MR 0132791 | 
Zbl 0111.03403 
[3] Kenneth M. Kapp: 
Green's Relations and Quasi-ideals. Czechoslovak Math. J. 19 (94) 1969, 80-85. 
MR 0238972 
[4] Kenneth M. Kapp: 
On Bi-ideals and Quasi-ideals in Semigroups. Publ. Math. Debrecen 16 (1969), 179-85. 
MR 0267018 
[5] Bruce W. Mielke: A Note on Bi-ideals and Quasi-ideals. to appear Publ. Math. Debrecen.
[6] O. Steinfeld: 
Über die Quasiideale von Halbgruppen. Publ. Math. Debrecen, 4 (1956), 262-275. 
MR 0083998 | 
Zbl 0070.25301 
[7] О. Steinfeld: 
Über die Quasiideale von Halbgruppen mit eigentlichem Suschkewitsch-Kern. Acta Sci. Math. Szeged 18 (1957), 235-242. 
MR 0095212 | 
Zbl 0079.02603