isbnGroup :: Gen String
isbnGroup = elements $ show <$> concat [
    [0..5] :: [Integer]
  , [7]
  , [80..94]
  , [600..621]
  , [950..989]
  , [9926..9989]
  , [99901..99976]
  ]
isbnGroup :: Gen String
isbnGroup = elements $ show <$> concat [
    [0..5] :: [Integer]
  , [7]
  , [80..94]
  , [600..621]
  , [950..989]
  , [9926..9989]
  , [99901..99976]
  ]
isbnGroup = elements $ show <$> concat [
    [0..5] :: [Integer]
  , [7]
  , [80..94]
  , [600..621]
  , [950..989]
  , [9926..9989]
  , [99901..99976]
  ]