@article{10_4064_cm87_2_5,
     author = {Leonid Makar-Limanov and Andrzej Nowicki},
     title = {On the ring of constants
for derivations of power series rings
in two variables},
     journal = {Colloquium Mathematicum},
     pages = {195--200},
     publisher = {mathdoc},
     volume = {87},
     number = {2},
     year = {2001},
     doi = {10.4064/cm87-2-5},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/cm87-2-5/}
}