Using M/F-theory duality, I will relate the quantization of the G-flux in M-theory to the one of the gauge flux on type IIB D7-branes prescribed by Freed-Witten anomaly cancellation. The correspondence is shown for all unitary and symplectic Kodaira singularities, by explicitly constructing appropriate 4-cycles in the M-theory elliptic fourfold, which are able to detect the global anomaly.
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