Function field theory of plane curves by dual curves

We study the structure of function fields of plane curves following our method developed previously (K. Miura and H. Yoshihara, 2000, J. Algebra 226, 283-294). Let K be the function field of a smooth plane curve C of degree d (greater than or equal to 4) and let K-p be a maximal rational subfield of K for P is an element of P-2. W, study the field extension K/K-p from a geometrical viewpoint. Especially, we give a sufficient condition that the Galois group of the Galois closure of K/K-p becomes a full symmetric group. (C) 2001 Academic Press.