26. 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 or mistake of fact the contract of which performance is sought is in terms different from that which the defendant supposed it to be when he entered into it;(b) where by fraud, mistake of fact, or surprise the defendant entered into the contract under a reasonable misapprehension as to its effect as between himself and the plaintiff;(c) where the defendant, knowing the terms of the contract and understanding its effect, has entered into it relying upon some misrepresentation by the plaintiff, or upon some stipulation on the plaintiff's part, which adds to the contract, but which he refuses to fulfil;(d) where the object of the parties was to produce a certain legal result, which the contract as framed is not calculated to produce;(e) where the parties have, subsequently to the execution of the contract, contracted to vary it.Illustrations (a) A, B and C sign a writing by which they purport to contract each to enter into a bond to D for taka 1,000. In a suit by D, to make A, B and C separately liable each to the extent of taka 1,000, they prove that the word "each" was inserted by mistake; that the intention was that should give a joint bound for taka 1,000. D can obtain the performance sought only with the variation thus set up. (b) A sues B to compel specific performance of a contract in writing to buy a dwelling-house. B proves that he assumed that the contract included and adjoining yard, and the contract was so framed as to leave it doubtful whether the yard was so included or not. The Court will refuse to enforce the contract, except with the variation set up by B. (c) A contracts in writing to let to B a wharf, together with a strip of A's land delineated in a map. Before signing the contract, B proposed orally that he should be at liberty to substitute for the strip mentioned in the contract another strip of A's land of the same dimensions, and to this A expressly assented. B then signed the written contract. A cannot obtain specific performance of the written contract, except with the variation set up by B. (d) A and B enter into negotiations for the purpose of securing land for B for his life, with remainder to his issue. They execute a contract, the terms of which are found to confer an absolute ownership on B. The contract so framed cannot be specifically enforced. (e) A contracts in writing to let a house to B, for a certain term, at the rent of taka 100 per month, putting it first into tenantable repair. The house turns out to be not worth repairing, so, with B's consent, A pulls it down and erects a new house in its place: B contracting orally to pay rent at taka 120 per mensem. B then sues to enforce specific performance of the contract in writing. He cannot enforce it except with the variations made by the subsequent oral contract.