uint256 private ptRate; // or PT price in asset (in Ray)
uint256 private ibtRate; // or IBT price in asset (in Ray)
uint256 private ptRate; // PT price in asset (in Ray)
uint256 private ibtRate; // IBT price in asset (in Ray)
  address private rewardsProxy;
  bool private ratesAtExpiryStored;
  address private ibt; // address of the Interest Bearing Token 4626 held by this PT vault
  address private _asset; // the asset of this PT vault (which is also the asset of the IBT 4626)
  address private yt; // YT corresponding to this PT, deployed at initialization
  uint256 private ibtUnit; // equal to one unit of the IBT held by this PT vault (10^decimals)
  uint256 private _ibtDecimals;
  uint256 private _assetDecimals;

  uint256 private ptRate; // or PT price in asset (in Ray)
  uint256 private ibtRate; // or IBT price in asset (in Ray)
  uint256 private unclaimedFeesInIBT; // unclaimed fees
  uint256 private totalFeesInIBT; // total fees
  uint256 private expiry; // date of maturity (set at initialization)
  uint256 private duration; // duration to maturity
