∀ {σ : Type u_1} {R : Type u_3} [inst : CommRing R] {τ : Type u_4} {S : Type u_5} [inst_1 : CommRing S]
  [inst_2 : Algebra R S] {a : σ → MvPowerSeries τ S},
  MvPowerSeries.HasSubst a →
    ∀ (f g : MvPowerSeries σ R), MvPowerSeries.subst a (f + g) = MvPowerSeries.subst a f + MvPowerSeries.subst a g