a b c : Int
h✝ : a < b + c
h : -b + a < -b + (b + c)
⊢ -b + a < c
a b c : Int
h : a < b + c
⊢ -b + a < c
have h := Int.add_lt_add_left h (-b)
no goals
a b c : Int
h✝ : a < b + c
h : -b + a < -b + (b + c)
⊢ -b + a < c
rwa [Int.neg_add_cancel_left] at h