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.

References

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


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