English
The leading coefficient equals the coefficient at the order: leadingCoeff(x) = coeff(x, order(x)).
Русский
Ведущий коэффициент равен коэффициенту при порядке: leadingCoeff(x) = coeff(x, order(x)).
LaTeX
$$$ \\operatorname{leadingCoeff}(x) = \\operatorname{coeff}(x, x.\\mathrm{order}) $$$
Lean4
theorem leadingCoeff_eq {x : HahnSeries Γ R} : x.leadingCoeff = x.coeff x.order :=
by
by_cases h : x = 0
· rw [h, leadingCoeff_zero, coeff_zero]
· simp [leadingCoeff_of_ne_zero, orderTop_of_ne_zero, order_of_ne, h]