1. Picone, M: Su un problema al contorno nelle equazioni differenziali lineari ordinarie del secondo ordine. Ann. Sc. Norm. Super. Pisa, Cl. Sci. 10, 1-95 (1908)
2. Boucherif, A: Nonlinear three-point boundary value problems. J. Math. Anal. Appl. 77, 577-600 (1980)
3. Štikonas, A: A survey on stationary problems, Green’s functions and spectrum of Sturm-Liouville problem with nonlocal boundary conditions. Nonlinear Anal., Model. Control 19, 301-334 (2014)
4. Conti, R: Recent trends in the theory of boundary value problems for ordinary differential equations. Boll. Unione Mat. Ital. 22, 135-178 (1967)
5. Ma, R: A survey on nonlocal boundary value problems. Appl. Math. E-Notes 7, 257-279 (2001)