We shall give the best possible upper bound of the Fano indices together with a characterization of those Q-Fano 3-folds which attain the maximum in terms of graded rings. 0. Introduction Q-Fano 3-folds play important roles in birational algebraic geometry. They have been studied by several authors since G. Fano. In this paper, we study Q-Fano 3-folds from the view of their Fano indices (See definition 0.2 below) and graded rings. More concretely, we give an optimal upper bound for the Fano… CONTINUE READING