The stabilizer bitorsors of the module and algebra harmonic coproducts are equal

In earlier work, we constructed a pair of “Betti” and “de Rham” Hopf algebras and a pair of module-coalgebras over this pair, as well as the bitorsors related to both structures (which will be called the “module” and “algebra” stabilizer bitorsors). We showed that Racinet's torsor constructed out of the double shuffle and regularization relations between multiple zeta values is essentially equal to the “module” stabilizer bitorsor, and that the latter is contained in the “algebra” stabilizer bitorsor. In this paper, we show the equality of the “algebra” and “module” stabilizer bitorsors. We reduce the proof to showing the equality of the associated “algebra” and “module” graded Lie algebras. The argument for showing this equality involves the relation of the “algebra” Lie algebra with the kernel of a linear map, the expression of this linear map as a composition of three linear maps, the relation of one of them with the “module” Lie algebra and the computation of the kernel of the other one by discrete topology arguments.