intro x
⊢ ∀ (x : ℝ × ℝ), x ∈ ⋂ α, ⋂ (_ : 0 ≤ α ∧ α ≤ 1), Set.Icc α 1 ×ˢ Set.Icc 0 α ↔ x ∈ Set.singleton (1, 0)
x : ℝ × ℝ
⊢ x ∈ ⋂ α, ⋂ (_ : 0 ≤ α ∧ α ≤ 1), Set.Icc α 1 ×ˢ Set.Icc 0 α ↔ x ∈ Set.singleton (1, 0)