epMaybe :: EP (Maybe a) (MaybeS a)
epMaybe = EP fromMaybe toMaybe
  where
    fromMaybe Nothing  =  L Unit
    fromMaybe (Just a) =  R a
    toMaybe (L Unit) =  Nothing
    toMaybe (R a)    =  Just a
epMaybe :: EP (Maybe a) (MaybeS a)
epMaybe = EP fromMaybe toMaybe
  where
    fromMaybe Nothing  =  L Unit
    fromMaybe (Just a) =  R a
    toMaybe (L Unit) =  Nothing
    toMaybe (R a)    =  Just a
epMaybe = EP fromMaybe toMaybe
  where
    fromMaybe Nothing  =  L Unit
    fromMaybe (Just a) =  R a
    toMaybe (L Unit) =  Nothing
    toMaybe (R a)    =  Just a