Abstract
This is a research proposal submitted to FAPESP for Hiêp Hàn's application for a postdoctoral fellowship at the Institute of Mathematics and Statistics of the University of São Paulo (IME/USP). Hàn's stay in São Paulo is initially planned for 24 months, from 4 January 2011. This researcher will be a member of the combinatorics and theory group at IME/USP and of NUMEC, Núcleo de Modelage…