Research proof index

An approximate-homomorphism theorem for finite elementary abelian $2$-groups. Let $f:G\to G'$ and $K>0$. If at least a proportion $K^{-1}$ of pairs $(x,y)\in G^2$ satisfy $f(x+y)=f(x)+f(y)$, then there are an additive homomorphism $\varphi:G\to G'$ and a constant $c\in G'$ such that $f(x)=\varphi(x)+c$ for at least $|G|/(2^{144}K^{122})$ values of $x$.

In the ambient finite $\mathbb F_2$-vector space, exactly half of the additive homomorphisms $\varphi:G\to\mathbb F_2$ take a fixed nonzero vector $x$ to $1$: $2\,|\{\varphi:\varphi(x)=1\}|=|G|$.

For every set $A$ in the ambient finite $\mathbb F_2$-vector space, some linear functional $\varphi:G\to\mathbb F_2$ has at least $(|A|-1)/2$ elements of $A$ in its $1$-fiber.