Normal curvatures and Euler classes for polyhedral surfaces in 4-space
Thomas Banchoff · Proceedings of the American Mathematical Society · 1984
Using the approach of singularities of projections into lower dimensional spaces it is possible to define nonintrinsic local curvature quantities at each vertex of a polyhedral surface immersed in 4 4 -space which add up to the normal Euler number of the immersion. Related uniqueness results for lattice polyhedra have been established by B. Yusin.