Superclass does not be inherited if same constraint was applied to different type parameter #3431

class (Functor f, Functor g) <= MyClass f g

fff :: forall f g. MyClass f g => f ~> f
fff = map identity -- Err, No type class instance was found for Functor f

ggg :: forall f g. MyClass f g => g ~> g
ggg = map identity -- ok

-- swap definition order f <-> g
class (Functor g, Functor f) <= MyClass f g

fff :: forall f g. MyClass f g => f ~> f
fff = map identity -- ok

ggg :: forall f g. MyClass f g => g ~> g
ggg = map identity -- Err, No type class instance was found for Functor g

-- g is not `Apply`
class (Apply f, Functor g) <= MyClass f g

ffff :: forall f g a b. MyClass f g => f (a -> b) -> f a -> f b
ffff = apply -- ok

-- g implies `Apply`
class (Apply f, Applicative g) <= MyClass f g

ffff :: forall f g a b. MyClass f g => f (a -> b) -> f a -> f b
ffff = apply -- Err, No type class instance was found for Apply f