have (And.intro (_ : n₁ ≤ n₂) (_ : n₁ ≄ n₂)) := lt_defn.mp ‹n₁ < n₂›
ℕ : Type
inst✝³ : Core ℕ
inst✝² : Induction ℕ
inst✝¹ : Addition ℕ
inst✝ : Sign ℕ
order_inst : Order ℕ
n₁ n₂ m : ℕ
x✝ : n₁ < n₂
⊢ n₁ + m < n₂ + m
ℕ : Type
inst✝³ : Core ℕ
inst✝² : Induction ℕ
inst✝¹ : Addition ℕ
inst✝ : Sign ℕ
order_inst : Order ℕ
n₁ n₂ m : ℕ
x✝ : n₁ < n₂
left✝ : n₁ ≤ n₂
right✝ : n₁ ≄ n₂
⊢ n₁ + m < n₂ + m