A Variant of Shokurov’s Criterion of Toric Surface
نویسندگان
چکیده
As a variant of Shokurov’s criterion of toric surface, we give a criterion of two new classes of normal projective surfaces, called pseudo-toric surfaces of defect one and half-toric surfaces. A typical example of pseudo-toric surface of defect one is the blown up of a projective toric surface at a nonsingular point of the boundary divisor. A half-toric surface is the quotient of a projective toric surface by an almost free involution preserving the boundary divisor. The structure of pseudo-toric surface of defect one and that of halftoric surface are also studied in detail.
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