English
The exponential function commutes with complex conjugation: exp(conj x) = conj(exp x).
Русский
Экспонента коммутирует со сложением по сопряжению: exp(conj x) = conj(exp x).
LaTeX
$$$exp(conj x) = conj (exp x)$$$
Lean4
@[simp]
theorem exp_conj : exp (conj x) = conj (exp x) := by
dsimp [exp]
rw [← lim_conj]
refine congr_arg CauSeq.lim (CauSeq.ext fun _ => ?_)
dsimp [exp', Function.comp_def, cauSeqConj]
rw [map_sum (starRingEnd _)]
refine sum_congr rfl fun n _ => ?_
rw [map_div₀, map_pow, ← ofReal_natCast, conj_ofReal]