@article{ASUO_2007_XV_2_a7,
     author = {W. Puninagool and S. Leeratanavalee},
     title = {
							{Idempotent} {Pre-Generalized} {Hypersubstitutions} of
							{Type} t = (2, 2)},
     journal = {Analele Universit\u{a}\c{t}ii "Ovidius" Constan\c{t}a Seria Matematic\u{a}},
     publisher = {mathdoc},
     volume = {XV},
     number = {2},
     year = {2007},
     url = {http://geodesic.mathdoc.fr/item/ASUO_2007_XV_2_a7/}
}