On varieties of almost minimal degree III: Tangent spaces and embedding scrolls

Abstract

Let X⊂Pr be a variety of almost minimal degree which is the projected image of a rational normal scroll View the MathML source from a point p outside of View the MathML source. In this paper we study the tangent spaces at singular points of X and the geometry of the embedding scrolls of X, i.e. the rational normal scrolls Y⊂Pr which contain X as a codimension one subvariety.