@article{PSMIR_1974___1_A3_0,
     author = {Bolley, P. and Camus, J. and Helffer, B.},
     title = {Op\'erateurs pseudo-diff\'erentiels \`a valeurs vectorielles. {Application} \`a l'\'etude de l'hypoellipticit\'e de certains op\'erateurs},
     journal = {Publications des s\'eminaires de math\'ematiques et informatique de Rennes},
     note = {talk:3},
     pages = {1--9},
     publisher = {D\'epartement de Math\'ematiques et Informatique, Universit\'e de Rennes},
     number = {1},
     year = {1974},
     language = {fr},
     url = {http://www.numdam.org/item/PSMIR_1974___1_A3_0/}
}