= Norman Steenrod
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<Norman Steenrod> developed operations on <cohomology> that reveal structure beyond the <cohomology> groups alone. His original work constructs the mod-two <Steenrod squares>, organized under composition in the <Steenrod algebra>.<Products of cocycles and extensions of mappings by Norman Steenrod>[Original paper and cochain-construction contribution]{ref}
An operation $Sq^i$ sends a class in degree $n$ to one in degree $n+i$ and behaves naturally under <continuous maps>. The top square satisfies $Sq^n(a)=a\smile a$, connecting the operations with the <cup product>. Such compatibility makes them useful for distinguishing spaces and detecting restrictions on maps, even when simpler algebraic invariants agree.
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