In this paper, we obtain several nonexistence results for abelian Hadamard diier-ence sets. In particular, we prove that there are no Hadamard diierence sets in abelian groups G = Z 2 Z 2 P , where jPj = p 2 , is odd and p is a prime congruent to 1(mod 4). Also we give a detailed proof for a connection between certain reversible Hadamard diierence sets and projective three-weight codes which wa...

Subdivision surfaces are considered which consist of tri-or quadrilateral patches in a mostly regular arrangement with nitely many irregularities. A sharp estimate on the lowest possible degree of the patches is given. It depends on the smoothness and exibility of the underlying subdivision scheme.