repeat rw [← sSup_image]
n : ℕ
f : Bump ℝ
K : Set ℝ
hK : IsCompact K
⊢ ⨆ x ∈ K, ↑(absNthDeriv n f x) = ⨆ a ∈ absNthDeriv n f '' K, ↑a
n : ℕ
f : Bump ℝ
K : Set ℝ
hK : IsCompact K
⊢ sSup ((fun x => ↑(absNthDeriv n f x)) '' K) = sSup ((fun a => ↑a) '' (absNthDeriv n f '' K))