Abstract. We say that a surface in Minkowski 3-space is a lightlike developable if all pseudo-normal vectors of the regular part of the surface are lightlike. The tangent surface of a lightlike curve is one of the lightlike developables. We give a generic classification of such surfaces. The all arguments in this paper are elementary. However, we discovered the H 3 type singularity appears in generic for such a class of surfaces. Since the H 3 type singularity usually appears in non-generic situation, this is a quite interesting phenomenon. IntroductionA surface in Euclidean space whose Gauss curvature vanishes on the regular part is called a developable surface. It has been known that a developable surface is a part of a conical surface, a cylindrical surface, the tangent surface of a space curve or the glue of such surfaces. Developable surfaces have singularities in general. The tangent surface of a space curve has the most interesting singularities in the above three kinds of surfaces. In fact Cleave [2] showed that the germ of the tangent surface of a generic cuspdialedge cuspidal cross cap 2000 Mathematics Subject Classification: 53A35, 58C27, 58C28.

Abstract. We say that a surface in Minkowski 3-space is a lightlike developable if all pseudo-normal vectors of the regular part of the surface sire lightlike. The tangent surface of a lightlike curve is one of the lightlike developables. We give a generic classification of such surfaces. The all arguments in this paper are elementary. However, we discovered the H3 type singularity appears in generic for such a class of surfaces. Since the H3 type singularity usually appears in non-generic situation, this is a quite interesting phenomenon. IntroductionA surface in Euclidean space whose Gauss curvature vanishes on the regular part is called a developable surface. It has been known that a developable surface is a part of a conical surface, a cylindrical surface, the tangent surface of a space curve or the glue of such surfaces. Developable surfaces have singularities in general. The tangent surface of a space curve has the most interesting singularities in the above three kinds of surfaces. In fact Cleave [2] showed that the germ of the tangent surface of a generic 2000 Mathematics Subject Classification: 53A35, 58C27, 58C28.