 Further, the rule applies not only to express terms (terms actually in the written contract), but also to terms implied by law.For example, where land is sold, an obligation to pay the costs of transfer is, in the absence of express provision to the contrary, imposed by law on the seller.It follows that, if a written contract of sale of land makes no reference to the costs of transfer, the seller is not allowed to give evidence of an alleged prior agreement with the purchaser that the latter is to pay these costs.