tranchePrice: returns the last tranche price saved on the last smart contract interaction (it may not include interest earned since the last update, for an up to date price check the virtualPrice method).
virtualPrice: calculates the current tranches price considering the interest that is yet to be split (i.e. the interest generated since the last interaction done on depositXX/withdrawXX/harvest, useful for showing updated gains on frontends.
withdrawAA: allows a user to burn a AA tranche token and get the principal + interest back (if no emergency shutdown is in progress).
withdrawBB: allows a user to burn a BB tranche token and get the principal + interest back (if no emergency shutdown is in progress).