Pierre B'erard

Level sets of certain Neumann eigenfunctions under deformation of Lipschitz domains Application to the Extended Courant Property

Bernard Helffer, Pierre B'erard, B. Helffer, 2018, Annales de la Faculté des sciences de Toulouse : Mathématiques.

Sturm’s theorem on zeros of linear combinations of eigenfunctions

Bernard Helffer, Pierre B'erard, B. Helffer, 2017, Expositiones Mathematicae.

Sturm's Theorem on the Zeros of Sums of Eigenfunctions: Gelfand's Strategy Implemented

Bernard Helffer, Pierre B'erard, B. Helffer, 2018, 1807.03990.