La propriété des corps
We give lower bounds on the number of effective divisors of degree with respect to the number of places of certain degrees of an algebraic function field of genus defined over a finite field. We deduce lower bounds for the class number which improve the Lachaud - Martin-Deschamps bounds and asymptotically reaches the Tsfasman-Vladut bounds. We give examples of towers of algebraic function fields having a large class number.