 Freiman-Ruzsa bound from Bogolyubov and linear modelling

Let $A$ be a nonempty subset of ${\mathbb{F}}_2^N$ with doubling constant at most $C\ge 1$. Translate to $B=A+a$ containing zero. The Petridis minimal-growth lemma and Ruzsa triangle inequality bound $|kB|\le C^k|B|$. In injective linear modelling of a small sumset, the image has density at least $1/(4C^{12})$. The Finite-field Bogolyubov lemma finds a subspace of codimension at most $\lceil 32C^{24}\rceil$ in its fourfold sumset.

After lifting a subspace through a Freiman model, obtain $\tilde{W}\subseteq 4B$ with $|\tilde{W}|\ge 2^{-\lceil 32C^{24}\rceil }|B|$. The set $B+\tilde{W}\subseteq 5B$ uses at most $C^5{2}^{\lceil 32C^{24}\rceil }$ cosets. Their representatives generate a quotient group of size at most two to this number. Since $|\tilde{W}|\le C^4|B|$, adjoining those representatives and $a$ proves the displayed bound. Its constants are deliberately coarse, but depend only on $C$. The nonempty assumption is necessary: no vector subspace has cardinality at most a constant times the size of the empty set.