On the multiplicity of the second eigenvalue of Laplacian in \(\mathbb{R}^ 2\)
Let \(\Omega\) be a bounded domain of \(\mathbb{R}^2\) with boundary that can be parametrized as a smooth function. Then the multiplicity of the second eigenvalue of \(\Delta\varphi+ \lambda\varphi= 0\) in \(\Omega\), \(\varphi= 0\) on \(\partial \Omega\) is at most two.
scientific article; zbMATH DE number 856917