Projective convexity in P-3 implies Grassmann convexity

In this note we introduce the notion of Grassmann convexity analogous to th e well-known notion of convexity for curves in real projective spaces. We s how that the curve in G(2,4) osculating to a convex closed curve in P-3 is Grassmann-convex. This proves that the tangent developable (i.e. the hypers urface formed by all tangents) of any convex curve in P-3 has the "degree" equal to 4. Here by "degree" of a real projective hypersurface we mean the maximal total multiplicity of its intersection with a line.