Very flat, locally very flat, and contraadjusted modules

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• 作者：Alexander Slá ; vik ^{Slavik.Alexander@seznam.cz" class="auth_mail" title="E-mail the corresponding author} ; Jan Trlifaj ; ^{trlifaj@karlin.mff.cuni.cz" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Primary ; 13C11 ; secondary ; 14F05 ; 16D70 ; 13E05 ; 13G05
• 刊名：Journal of Pure and Applied Algebra
• 出版年：2016
• 出版时间：December 2016
• 年：2016
• 卷：220
• 期：12
• 页码：3910-3926
• 全文大小：451 K

文摘

Very flat and contraadjusted modules naturally arise in algebraic geometry in the study of contraherent cosheaves over schemes. Here, we investigate the structure and approximation properties of these modules over commutative noetherian rings. Using an analogy between projective and flat Mittag-Leffler modules on one hand, and very flat and locally very flat modules on the other, we prove that each of the following statements are equivalent to the finiteness of the Zariski spectrum Spec(R)$\mathrm{Spec}(R)$ of a noetherian domain R: (i) the class of all very flat modules is covering, (ii) the class of all locally very flat modules is precovering, and (iii) the class of all contraadjusted modules is enveloping. We also prove an analog of Pontryagin's Criterion for locally very flat modules over Dedekind domains.