getDiacriticalCommand  :: Position -> String -> Maybe String
getDiacriticalCommand pos symbol = do
  command <- M.lookup symbol diaMap
  guard (not $ command `elem` unavailable)
  let below = command `elem` under
  case pos of
    Under -> if below then Just command else Nothing
    Over -> if not below then Just command else Nothing
  where
    diaMap = M.fromList diacriticals

-- Operator Table
getDiacriticalCommand  :: Position -> String -> Maybe String
getDiacriticalCommand pos symbol = do
  command <- M.lookup symbol diaMap
  guard (not $ command `elem` unavailable)
  let below = command `elem` under
  case pos of
    Under -> if below then Just command else Nothing
    Over -> if not below then Just command else Nothing
  where
    diaMap = M.fromList diacriticals

-- Operator Table
getDiacriticalCommand pos symbol = do
  command <- M.lookup symbol diaMap
  guard (not $ command `elem` unavailable)
  let below = command `elem` under
  case pos of
    Under -> if below then Just command else Nothing
    Over -> if not below then Just command else Nothing
  where
    diaMap = M.fromList diacriticals

-- Operator Table