@article{701621,
     title = {Natural operators on vector fields on the cotangent bundles of the bundles of $(k,r)$-velocities},
     booktitle = {Proceedings of the 17th Winter School "Geometry and Physics"},
     series = {GDML\_Books},
     publisher = {Circolo Matematico di Palermo},
     address = {Palermo},
     year = {1998},
     pages = {[113]-124},
     mrnumber = {MR1662732},
     zbl = {0929.58001},
     url = {http://dml.mathdoc.fr/item/701621}
}

Tomáš, Jiří. Natural operators on vector fields on the cotangent bundles of the bundles of $(k,r)$-velocities, dans Proceedings of the 17th Winter School "Geometry and Physics", GDML_Books,  (1998), pp. [113]-124. http://gdmltest.u-ga.fr/item/701621/