inferType d g (ELetRGN tr1 ta v) =
  case (inferType d g . valToExp) v of 
    Nothing -> Nothing
    Just (FForall gr2 (FArrow (FArrow (FArrow (RGN tr1 (FVar gr2')) (RGN (FVar gr2'') gr2''')) (RGNHandle (FVar gr2''''))) (RGN (FVar gr2''''') ta)))  
      | (S.member tr1 d) && (S.member ta d) && gr2 == gr2' && gr2' == gr2'' && gr2'' == gr2''' && gr2''' == gr2'''' && gr2'''' == gr2''''' ->  Just $ RGN tr1 ta
      | otherwise -> Nothing