@article{SIGMA_2009_5_a93,
     author = {Igor Zelenko},
     title = {On {Tanaka's} {Prolongation} {Procedure} for {Filtered} {Structures} of {Constant} {Type}},
     journal = {Symmetry, integrability and geometry: methods and applications},
     year = {2009},
     volume = {5},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SIGMA_2009_5_a93/}
}