55) On singularities of mappings of Euclidean spaces. |. Mappings of the plane into the plane. Ann. Math. 62:374-410 Whittington, M.A., Traub, R.D., Jefferys, J.G.R. (1995): Synchronized oscillations in interneuron networks driven by metabotropic glutamate receptor activation. Nature 373:612-615 Wiggins, S. (1990