On the Focal Locus of a Submanifold in a Riemannian Manifold of Constant Sectional Curvature Hukum Singh — 1985 Publications de l'Institut Mathématique
On the Generalized Gauss Lemma in Lorentzian Manifolds Hukum Singh — 1985 Publications de l'Institut Mathématique
On the cut locus and the focal locus of a submanifold in a Riemannian manifold. II. Singh, Hukum — 1987 Publications de l'Institut Mathématique. Nouvelle Série