Ample Sheaves on Group Homogeneous Spaces Over Prufer Bases

In this note, we study invertible sheaves on group homogeneous spaces and their ampleness, especially when the bases are Prufer schemes, namely, the schemes whose all local rings are valuation rings. First, we give several conditions for Hartogs's phenomenon of invertible sheaves to hold on non-Noetherian schemes through parafactorial pairs in EGAIV4, thus describe relatively effective Cartier divisors on smooth schemes over valuation rings as flat closed subschemes of pure codimension one. Subsequently, we obtain criteria for ampleness in the non-Noetherian case, and from this, construct ample invertible sheaves explicitly in terms of the flat cycles of pure codimension one. Finally, we establish extension properties of (semi)ample invertible sheaves on group homogeneous spaces smooth over Prüferian bases.