3 problems

Let $L(V)$ be the operator considered in the paper, with Bloch eigenvalues depending on $V$. A Bloch eigenvalue is said to leave the real line when it becomes nonreal as $V$ varies…

Let $H(c)$ be the operator with pure imaginary potential $2ic\cos 2x$, and let $L(V)$ be the corresponding operator whose Bloch eigenvalues depend on $V$. Leaving principle. If $c$…

Let $E$ be the linear operator in the layer-potential system for the unknown densities $[\eta;\xi]$, where $\eta=[\tau;-\sigma]$, and let $(\omega,a,b)$ denote the frequency and qu…