use fun h ↦ ⟨h (left_mem_rect z' w'), h (right_mem_rect z' w')⟩
z✝ w✝ : ℂ
c : ℝ
z w z' w' : ℂ
⊢ Rectangle z' w' ⊆ Rectangle z w ↔ z' ∈ Rectangle z w ∧ w' ∈ Rectangle z w
case mpr
z✝ w✝ : ℂ
c : ℝ
z w z' w' : ℂ
⊢ z' ∈ Rectangle z w ∧ w' ∈ Rectangle z w → Rectangle z' w' ⊆ Rectangle z w