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{wiki=Cartan_formula#Cartan_formula_in_algebraic_topology}

= Cartan formula
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The Cartan product formula says that total <Steenrod squares> and total <Steenrod reduced powers> preserve the <cup product>:
$$
\operatorname{Sq}^k(ab)=\sum_{i+j=k}\operatorname{Sq}^i(a)\operatorname{Sq}^j(b),
\qquad
P^k(ab)=\sum_{i+j=k}P^i(a)P^j(b).
$$
It is named after Henri Cartan and is distinct from <Cartan's magic formula> for the <Lie derivative of a differential form>, named after Élie Cartan.


Cartan formula

Cartan formula (algebraic topology)

codex/cartan-formula

Cartan formula (algebraic topology)

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Cartan formula (algebraic topology)

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