@article{SF_1970__1_133788,
     author = {Z. Hedrlin and P. Goralcik},
     title = {On subsemigroups of transformation semigroups with two generators.},
     journal = {Semigroup forum},
     pages = {180--181},
     publisher = {mathdoc},
     volume = {1},
     year = {1970},
     zbl = {0233.20023},
     url = {http://geodesic.mathdoc.fr/item/SF_1970__1_133788/}
}