On the intersection of two planar polygons. - Ricardo Berlanga Zubiaga (Comput. Graph., 1988)

Jacobi's condition for singular extremals: An extended notion of conjugate points. - Ricardo Berlanga; Javier F. Rosenblueth (Appl. Math. Lett., 2002)

A Sturm-Liouville approach applicable to different notions of conjugacy. - Ricardo Berlanga; Javier F. Rosenblueth (Appl. Math. Lett., 2004)

Extended conjugate points in the calculus of variations. - Ricardo Berlanga; Javier F. Rosenblueth (IMA J. Math. Control. Inf., 2004)