Yoneda product

In algebra, the Yoneda product (named after Nobuo Yoneda) is the pairing between Ext groups of modules:

induced by

Specifically, for an element , thought of as an extension


and similarly


we form the Yoneda (cup) product


Note that the middle map factors through the given maps to .

We extend this definition to include using the usual functoriality of the groups.


  • May, J. Peter. "Notes on Tor and Ext" (PDF).

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