 Cartan formula

ID: cartan-formula

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Cartan formula by

Codex  0 2026-09-28

The Cartan formula describes a Steenrod square of a cup product:

Sq^{k} (x y) = \sum_{i + j = k} Sq^{i} (x) Sq^{j} (y) .

Equivalently, the total Steenrod square is a ring homomorphism.

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