simp only [subset_inter_iff, inter_subset_left, inter_subset_right, and_self,
  and_true, t]
case h
f : ℝ → ℝ
a x : ℝ
f_mono : StrictMono f
f_iso : Isometry f
v u : Set ℝ
hu : IsOpen u
hu2 : f x + a ∈ u
hu3 : u ∩ Ioi (f x + a) ⊆ v
t : Set ℝ := {x | f x + a ∈ u}
⊢ IsOpen t ∧ x ∈ t ∧ t ∩ Ioi x ⊆ t ∩ Ioi x
case h
f : ℝ → ℝ
a x : ℝ
f_mono : StrictMono f
f_iso : Isometry f
v u : Set ℝ
hu : IsOpen u
hu2 : f x + a ∈ u
hu3 : u ∩ Ioi (f x + a) ⊆ v
t : Set ℝ := {x | f x + a ∈ u}
⊢ IsOpen {x | f x + a ∈ u} ∧ x ∈ {x | f x + a ∈ u}