@article{MZM_1968_3_6_a4,
     author = {E. S. Lyapin},
     title = {Defining relations of semigroups of all directed transformations of an~ordered finite set},
     journal = {Matemati\v{c}eskie zametki},
     pages = {657--662},
     year = {1968},
     volume = {3},
     number = {6},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1968_3_6_a4/}
}