dsimp [flip]
case a
α : Type u
inst✝¹ : LinearLT α
inst✝ : DecidableRel LT.lt
x y : FreeCMonoid α
⊢ KVChain.mergeWith (fun a => flip fun a b => some (valAdd a b)) y.vars x.vars =
    KVChain.mergeWith (fun x a b => some (valAdd a b)) y.vars x.vars
case a
α : Type u
inst✝¹ : LinearLT α
inst✝ : DecidableRel LT.lt
x y : FreeCMonoid α
⊢ KVChain.mergeWith (fun a b a => some (valAdd a b)) y.vars x.vars =
    KVChain.mergeWith (fun x a b => some (valAdd a b)) y.vars x.vars