-- data instance Family Int (a, b) a = FamilyInt a b
checkFm0 :: Lens (Family Int (a, b) a) (Family Int (a', b') a') (b, a) (b', a')
checkFm0 = fm0
checkFm0 :: Lens (Family Int (a, b) a) (Family Int (a', b') a') (b, a) (b', a')
checkFm0 = fm0
checkFm0 = fm0