This paper is about a small combinatorial trick, which is well known, but has
no name. Let G be a permutation group acting on a vector space M. There is a
natural way to assign a cosimplicial space to these data. We call the resulting
cochain complex the cubical complex. Its cohomology is easy to compute. We give
some examples of its occurrence in nature.
We show that the zeroth cohomology of Kontsevich's graph complex is
isomorphic to the Grothendieck-Teichm\"uller Lie algebra grt. The map is
explicitly described. This result has applications to deformation quantization
and Duflo theory. Also, it allows proving the freeness part of the
Deligne-Drinfeld conjecture in some low orders. As a side result one obtains
that the homotopy deformations of the Gerstenhaber operad are parameterized by
grt. Finally, our methods give a second proof of a result of H.
The aim of this short note is to present a proof of Conjecture 1.3 of
\cite{CFFR} about the existence of an $A_\infty$-quasi-isomorphism between the
$A_\infty$-$\mathrm S(V^*)$-$\wedge(V)$-bimodule $K$, introduced in
\cite{CFFR}, and the Koszul complex $\mathrm K(V)$ of $\mathrm S(V^*)$, viewed
as a $\mathrm S(V^*)$-$\wedge(V)$-bimodule, for $V$ a finite-dimensional
(complex or real) vector space.