type E :: * -> * -> *
type family E a b where
    E a a = ()
    E a b = Bool
  	-- Defined at <interactive>:2:1
type E :: * -> * -> *
type family E a b where
  {- #0 -} E a a = ()
  {- #1 -} E a b = Bool
      -- incompatible with: #0
  	-- Defined at <interactive>:2:1