# Yoneda product

In algebra, the **Yoneda product** 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, Notes on Tor and Ext

## External links

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