18. Non-enforcement except with variation.- Where a plaintiff seeks specific performance of a contract in writing, to which the defendant sets up a variation, the plaintiff cannot obtain the performance sought, except with the variation so set up, in the following cases, namely:-
(a) where by fraud, mistake of fact or misrepresentation, the written contract of which performance is sought is in its terms or effect different from what the parties agreed to, or does not contain all the terms agreed to between the parties on the basis of which the defendant entered into the contract;
(b) where the object of the parties was to produce a certain legal result which the contract as framed is not calculated to produce;
(c) where the parties have, subsequently to the execution of the contract, varied its terms.
19. Relief against parties and persons claiming under them by subsequent title.-Except as otherwise provided by this Chapter, specific performance of a contract may be enforced against-
(a)either party thereto;
(b) any other person claiming under him by a title arising subsequently to the contract, except a transferee for value who has paid his money in good faith and without notice of the original contract;
(c) any person claiming under a title which, though prior to the contract and known to the plaintiff, might have been displaced by the defendant;
(ca) when a limited liability partnership has entered into a contract and subsequently becomes amalgamated with another limited liability partnership, the new limited liability partnership which arises out of the amalgamation;
(d) when a company has entered into a contract and subsequently becomes amalgamated with another company, the new company which arises out of the amalgamation;
(e) when the promoters of a company have, before its incorporation, entered into a contract for the purpose of the company and such contract is warranted by the terms of the incorporation, the company:
Provided that the company has accepted the contract and communicated such acceptance to the other party to the contract.