Necessary and sufficient conditions for the local solvability in hyperfunctions of a class of systems of complex vector fields.
Necessary conditions for strong hyperbolicity of first order systems
Neuer und directer Beweis eines Fundamentalsatzes der Invariantentheorie.
Non completely solvable systems of complex first order PDEs
Note on the solution of transport equation by Tau method and Walsh functions.
Noyaux élémentaires d'équations aux dérivées partielles du premier ordre