Bohr-Sommerfeld conditions for several commuting Hamiltonians
  The goal of this paper is to find the quantization conditions of Bohr-Sommerfeld of k quantum Hamiltonians acting on the euclidian space of dimension n, depending on a small parameter h, and which commute to each other. That is we determine, around a regular energy level E of the euclidian space of dimension k the principal term of the asymptotics in h of the eigenvalues of the operators that are associated to a common eigenfunction. Thus we localize the so-called joint spectrum of the operators.   Under the assumption that the classical Hamiltonian flow of the joint principal symbol is periodic with constant periods on the energy level of E(a submanifold of codimension k) we prove that the part of the joint spectrum lying in a small neighbourhood of E is localized near a lattice of size h determined in terms of actions and Maslov indices. The multiplicity of the spectrum is also determined. 
C. Anne, A-M. Charbonnel