Crank-Nicolson stability on a finite Dirichlet interval

If $L$ is the negative semidefinite Dirichlet discrete Laplacian, the Crank-Nicolson amplification matrixhas eigenvalues $(1+\mu {\lambda }_j/2)/(1-\mu {\lambda }_j/2)$ of modulus at most one for every $\mu \ge 0$.