2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/160752We prove an analogue of Pleijel's nodal domain theorem for piecewise analytic planar domains with Neumann boundary conditions. This confirms a conjecture made by Pleijel in 1956. The proof is a combination of Pleijel's original approach and an estimate due to Toth and Zelditch for the number of boundary zeros of Neumann eigenfunctions.4 pages; to appear in the Proceedings of the AMSSpectral TheoryAnalysis of PDEs35B05; 35P99text