How is revocation carried out according to Article 270? 
Revocation is carried out through offer and acceptance in the session (majlis), along with receiving back the thing contracted for. The revocation is valid if the subject matter of the contract exists and is in the possession of the contracting party at the time of revocation. If part of the subject matter has been lost, the revocation is still valid as to the remaining part to the extent of the consideration attributable to it.