Further improvements on the designed minimum distance of algebraic geometry codes

In the literature about algebraic geometry codes one finds a lot of results improving Goppa�s minimum distance bound. These improvements often use the idea of �shrinking� or �growing� the defining divisors of the codes under certain technical conditions. The main contribution of this article is to show that most of these improvements can be obtained in a unified way from one (rather simple) theorem. Our result does not only simplify previous results but it also improves them further.