@article{SF_1980__20_134411,
     author = {H. L\"anger},
     title = {The free algebra in the variety generated by quasi-trivial semigroups},
     journal = {Semigroup forum},
     pages = {151--156},
     publisher = {mathdoc},
     volume = {20},
     year = {1980},
     zbl = {0441.20038},
     url = {http://geodesic.mathdoc.fr/item/SF_1980__20_134411/}
}