  The following question is proposed in [4, Question 1.20]: Let $G$ be a
compact group, and suppose that $$\mathcal{N}_k(G) = \{(x1,\dots,x_{k+1}) \in
G^{k+1} \;\|; [x_1,\dots, x_{k+1}] = 1\}$$ has positive Haar measure in
$G^{k+1}$. Does $G$ have an open $k$-step nilpotent subgroup? The case $k = 1$
is already known. We positively answer it for $k = 2$.
