English
For mv power series a, HasSubst a is equivalent to HasSubst (const Unit a).
Русский
Для многопеременного степенного ряда a, HasSubst a эквивалентно HasSubst (константный элемент Unit a).
LaTeX
$$$\mathrm{HasSubst}(a) \iff \mathrm{MvPowerSeries.HasSubst}(\mathrm{Function.const}\,\mathrm{Unit}\,a)$$$
Lean4
theorem hasSubst_iff {a : MvPowerSeries τ S} : HasSubst a ↔ MvPowerSeries.HasSubst (Function.const Unit a) :=
⟨fun ha ↦ MvPowerSeries.hasSubst_of_constantCoeff_nilpotent (Function.const Unit ha), fun ha ↦ (ha.const_coeff ())⟩