parts of a contract that survive past the transaction

Examples:

1. When one section of a contract is invalid, the rest of the contract "survives" and is still valid
2. If you were to buy someone's house today and the property taxes have not been paid yet, the owner would hand you 300 dollars for the future payment. When time comes for the payment, it is really 400 that the owner owes you, they still have to pay this 400; that part of the contract "survives"