apply Asymptotics.IsBigO.trans_le (g' := fun _ ↦ (0 : ℝ)) ?_ (by simp)
case h.refine_2
𝕂 : Type u_1
inst✝ : _root_.RCLike 𝕂
Ψ : ℝ → ℝ
diffΨ : ContDiff ℝ 1 Ψ
suppΨ : Function.support Ψ ⊆ Icc (1 / 2) 2
mass_one : ∫ (x : ℝ) in Ioi 0, Ψ x / x = 1
⊢ (fun x => ↑(Ψ x)) =O[atTop] fun x => x ^ (-1)
𝕂 : Type u_1
inst✝ : _root_.RCLike 𝕂
Ψ : ℝ → ℝ
diffΨ : ContDiff ℝ 1 Ψ
suppΨ : Function.support Ψ ⊆ Icc (1 / 2) 2
mass_one : ∫ (x : ℝ) in Ioi 0, Ψ x / x = 1
⊢ (fun x => ↑(Ψ x)) =O[atTop] fun x => 0