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 A null focal theorem on Lorentz manifolds Bull. Korean Math. Soc. 2001 Vol. 38, No. 2, 273-284 Jae-Up So Chonbuk National University Abstract : Let $P$ be a spacelike $(n-2)$-dimensional submanifold of an $n$-dimensional Lorentz manifold $M$ and let $\sigma$ be a $P$-normal null geodesic with $Ric(\sigma',\, \sigma') \geq m$, for any given nonpositive constant $m$. We establish a sufficient condition such that there is a focal point of $P$ along $\sigma$. Keywords : Lorentz manifold, null geodesic, focal point, warped product MSC numbers : 53C50 Downloads: Full-text PDF