class X a b where {
  xfoo :: a -> b;
}

class X a b => C a b where {
  cfoo :: a -> b -> b;
}

class Y a where {
  yfoo :: a -> Int;
}

instance X a Int where {
  xfoo x = 42;
}

instance Y a => C a Int where {
  cfoo x y = yfoo x + xfoo x + y;
}


f x = cfoo x 42;