English
Two multivariate power series are equal if all their coefficients are equal.
Русский
Две многовекторные формальные степенные серии равны, если равны все их коэффициенты.
LaTeX
$$$\\phi = \\psi \\;\\text{если}\\; \\forall n, \\mathrm{coeff}(n)\\,\\phi = \\mathrm{coeff}(n)\\,\\psi$$$
Lean4
/-- Two multivariate formal power series are equal if all their coefficients are equal. -/
@[ext]
theorem ext {φ ψ : MvPowerSeries σ R} (h : ∀ n : σ →₀ ℕ, coeff n φ = coeff n ψ) : φ = ψ :=
funext h