A martingale approach for P\'olya urn processes

This paper is devoted to a direct martingale approach for P{'o}lya urn models asymptotic behaviour. A P{'o}lya process is said to be small when the ratio of its remplacement matrix eigenvalues is less than or equal to 1/2, otherwise it is called large. We find again some well-known results on the asymptotic behaviour for small and large urns processes. We also provide new almost sure properties for small urns processes.