  On a flat manifold, M. Kontsevich's formality quasi-isomorphism is compatible
with cup-products on tangent cohomology spaces, in the sense that its
derivative at any formal Poisson 2-tensor induces an isomorphism of graded
commutative algebras from Poisson cohomology space to Hochschild cohomology
space relative to the associated deformed multiplication. We give here a
detailed proof of this result, with signs and orientations precised.
