What are the contracts which cannot be specifically enforced under the Specific Relief Act, 1963?

Following contracts cannot be specifically enforced under Specific Relief Act: Where a party to the contract has obtained substituted performance of a contract in accordance with the provisions of section 20 of the Specific Relief Act. A contract, the performance of which involves the performance of a continuous duty which the Court cannot supervise. A contract that is so dependent on the personal qualifications of the parties that the Court cannot enforce specific performance of its material terms. A contract which is in its nature determinable.