A comodule-bialgebra structure for word-series substitution and mould   composition
  An internal coproduct is described, which is compatible with Hoffman's quasi-shuffle product. Hoffman's quasi-shuffle Hopf algebra, with deconcatenation coproduct, is a comodule-Hopf algebra over the bialgebra thus defined. The relation with J. Ecalle's mould calculus, i.e. mould composition and contracting arborification, is precised. 
Kurusch Ebrahimi-Fard, Fr\'ed\'eric Fauvet, Dominique Manchon
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