Theorem 2.15
(Bogolyubov’s lemma)
.
Assuming that:
A
⊆
𝔽
p
n
be a set of density
α
Then
there exists
V
≤
𝔽
p
n
of codimension
≤
2
α
−
2
such that
V
⊆
A
+
A
−
A
−
A
.