Iterated derivations and the Leibniz rule
TheoremIterated derivation of a power when \(D\varepsilon = r\varepsilon^2\)#✓fully proved
Derivation.iterate_pow_of_apply_eq_smul_sq
If D epsilon = r • epsilon², then the nth iterate of D on epsilon^m has
coefficient r^n times the ascending factorial of m. The coefficient is not cancelled,
so the formula remains valid in positive characteristic.
theorem iterate_pow_of_apply_eq_smul_sq (D : Derivation R A A) (r : R) (epsilon : A)
(h : D epsilon = r • epsilon ^ 2) (n m : ℕ) :
(D : A → A)^[n] (epsilon ^ m) =
(r ^ n * (m.ascFactorial n : R)) • epsilon ^ (m + n)
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