have : n < m := compare_lt.mp ‹compare n m = Ordering.lt›
ℕ : Type
inst✝⁴ : Core ℕ
inst✝³ : Induction ℕ
inst✝² : Addition ℕ
inst✝¹ : Sign ℕ
order_inst : Order ℕ
inst✝ : Compare ℕ
ord : Ordering
n m k j : ℕ
x✝¹ : compare n m = Ordering.lt
x✝ : compare k j = Ordering.lt
⊢ compare (n + k) (m + j) = Ordering.lt
ℕ : Type
inst✝⁴ : Core ℕ
inst✝³ : Induction ℕ
inst✝² : Addition ℕ
inst✝¹ : Sign ℕ
order_inst : Order ℕ
inst✝ : Compare ℕ
ord : Ordering
n m k j : ℕ
x✝¹ : compare n m = Ordering.lt
x✝ : compare k j = Ordering.lt
this : n < m
⊢ compare (n + k) (m + j) = Ordering.lt