T7609.hs:7:16:
Expecting one more argument to ‘Maybe’
The second argument of a tuple should have kind ‘*’,
but ‘Maybe’ has kind ‘* -> *’
In the type signature for ‘f’: f :: (a `X` a, Maybe)
T7609.hs:10:7:
Expected a constraint, but ‘a `X` a’ has kind ‘*’
In the type signature for ‘g’: g :: (a `X` a) => Maybe