rw [←symm, cmp]
α : Type
inst✝ : Order α
x y : α
h : ¬compare y x = Ordering.lt
cmp : compare x y = Ordering.gt
⊢ compare y x = Ordering.lt
α : Type
inst✝ : Order α
x y : α
h : ¬compare y x = Ordering.lt
cmp : compare x y = Ordering.gt
⊢ Ordering.gt.swap = Ordering.lt