@book{11134,
	author = {Conference on "Approximation of Eigenvalues of Differential Operators", Vanderbilt Univ., Nashville, June 26-30, 1972 and Weinberger, Hans F.},
	title = {Variational methods for eigenvalue approximations},
	publisher = {SIAM,},
	year = {1974},
	address = {Philadelphia:}
}