by L. Lov鈇sz and M.D. Plummer. by M. Platt, and A.F. Carter. H. C. Torrey and G. A. Whitmer. by M. W. Porter and R. C. Spiller. by J. Kroonen and D. Vander. by K. Yano and S. Bochner. by S. Timoshenko and J.N. Goodier.