Flat Mittag-Leffler modules over countable rings
classification
🧮 math.RA
math.AG
keywords
flatmodulesmittag-lefflerclasscountabledoubleringaroch
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We show that over any ring, the double Ext-orthogonal class to all flat Mittag-Leffler modules contains all countable direct limits of flat Mittag-Leffler modules. If the ring is countable, then the double orthogonal class consists precisely of all flat modules and we deduce, using a recent result of \v{S}aroch and Trlifaj, that the class of flat Mittag-Leffler modules is not precovering in Mod-R unless R is right perfect.
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