  We describe in this note a torsor structure arising on the affine scheme
defined by a system of rationnal algebraic relations between polyzetas at roots
of unity (values of hyperlogarithmic functions on a fixed finite group of
complex roots of unity).
  When this group is reduced to 1, we call these numbers the polyzetas. They
generalize the values of the Riemann zeta function at odd positive integers and
are also called MZVs, multizetas, multiple harmonic series or Euler/Zagier
sums. It is believed that the relations we consider here span all algebraic
relations between them. The torsor structure underlying these relations should
in that case be se same as Drinfeld's torsor made of the Grothendieck-
Teichmueller group acting on associators.
  The formulas for the general case are derived from the action of the absolute
Galois group on the projective line minus finitely many points. It is an easy
consequence of the torsor structure that the algebra defined by these relations
is a polynomial algebra. This was stated first by J. Ecalle in the polyzetas
case.
