For example, when a contract is signed as consideration, the parties may perform it on entirely different dates. In this scenario, the use of a so-called “ab” formula may be appropriate. In addition, if the performance of the contract took place before the performance of the contract, there may be sufficient reason to postpone the date of entry into force of the treaty. If the document adds something that “should have been done” but was not done, usually for tax or similar reasons, then the position is simple. For example, if a seller sold their home in December, the seller could have benefited from certain tax benefits. However, he does not realize this until January and therefore wishes to send the document back to December. . . .