α✝ : Sort u_1
x₁ x₂ y₂ : α✝
h₂ : x₂ = y₂
⊢ x₁ = x₂ ↔ x₁ = y₂
α✝ : Sort u_1
x₁ y₁ x₂ y₂ : α✝
h₁ : x₁ = y₁
h₂ : x₂ = y₂
⊢ x₁ = x₂ ↔ y₁ = y₂
subst h₁
α✝ : Sort u_1
x₁ x₂ : α✝
⊢ x₁ = x₂ ↔ x₁ = x₂
α✝ : Sort u_1
x₁ x₂ y₂ : α✝
h₂ : x₂ = y₂
⊢ x₁ = x₂ ↔ x₁ = y₂
subst h₂
no goals
α✝ : Sort u_1
x₁ x₂ : α✝
⊢ x₁ = x₂ ↔ x₁ = x₂
rfl