Flexible polyhedra in Minkowski 3-space

 We prove that (non-immersed) flexible polyhedra do exist in the Minkowski 3-space and each of them preserves the (generalized) volume and the (total) mean curvature during a flex. To prove the latter result, we introduce the notion of the angle between two arbitrary non-null nonzero vectors in the Minkowski plane. Received: 16 August 2001 Published online: 19 May 2003 Mathematics Subject Classification (2000): 52C25, 51B20, 52B70, 52B11, 51M25