This paper studies
eigenvalues of elliptic operators on a bounded domain in a Euclidean space. We
obtain lower bounds for the eigenvalues of elliptic operators of higher orders
with Navier boundary condition. We also prove lower bounds and universal
inequalities of Payne–Pólya–Weinberger–Yang type for the eigenvalues of
second order elliptic equations in divergence form with Dirichlet boundary
condition.