On double coverings of a pointed non-singular curve with any Weierstrass semigroup

Abstract

Let $H$ be a Weierstrass semigroup, i.e., the set $H(P)$ of integers which are pole orders at $P$ of regular functions on $C \setminus \{P\}$ for some pointed non-singular curve $(C, P)$. In this paper for any Weierstrass semi group $H$ we construct a double covering $\pi:\tilde{C} \to C$ with a ramification point $\tilde{P}$ such that $H(\pi(\tilde{P})) = H$. We also determine the semigroup $H(\tidle{P})$. Moreover, in the case where $H$ starts with 3 we investigate the relation between the semigroup $H(\tilde{P})$ and the Weierstrass semigroup of a total ramification point on a cyclic covering of the projective line with degree 6.