@article{MZM_2000_67_2_a2,
     author = {V. G. Durnev},
     title = {Undecidability of a~simple fragment of a~positive theory with a~single constant for a~free semigroup of rank two},
     journal = {Matemati\v{c}eskie zametki},
     pages = {191--200},
     publisher = {mathdoc},
     volume = {67},
     number = {2},
     year = {2000},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_2000_67_2_a2/}
}