concrete GrammarGre of Grammar = 
  VerbGre, 
  NounGre, 
  SentenceGre,
  PhraseGre,
  StructuralGre,
  RelativeGre,
  AdjectiveGre,
  ConjunctionGre,
  NumeralGre,
  AdverbGre, 
  TenseGre,
  TextGre,
  IdiomGre,
  QuestionGre
  ;