-- definition
class Functor f where
fmap :: (a -> b) -> f a -> f b

-- methods
(<$) :: a -> f b -> f a (<$) = fmap . const
 fmap id $\ \leftrightsquigarrow\$ id fmap f . fmap g $\ \leftrightsquigarrow\$ fmap (f . g)

Discussion

In Haskell, the first law implies the second.