  Functors from (co)operads to bialgebras relate Hopf algebras that occur in
renormalisation to operads, which simplifies the proof of the Hopf algebra
axioms, and induces a characterisation of the corresponding group of characters
and Lie algebra of primitives of the dual in terms of the operad. In addition,
it is shown that the Wick rotation formula leads to canonical algebras for one
of these operads.
