. exact Eq.le rfl
case x.right
x : ℝ
hx : x ∈ Set.Ioo 0 (Real.pi / 2)
y' : ℝ → ℝ := fun x => (x - Real.pi / 4).tan
h4 : (Real.pi / 4).tan = y' (Real.pi / 2)
y1 : ℝ → ℝ := fun x => x - Real.pi / 4
h5 : StrictMonoOn y1 (Set.Icc 0 (Real.pi / 2))
h6 : StrictMonoOn y' (Set.Icc 0 (Real.pi / 2))
⊢ Real.pi / 2 ≤ Real.pi / 2
no goals