Post-contractual conduct is admissible to prove the existence and terms of a contract, to identify its subject matter, and as informal admissions of fact, even though it is not admissible on the interpretation of a contract. A Jones v Dunkel inference is not warranted where the evidence the uncalled witness could have given is already before the court through cross-examination admissions. For informal contracts, a term will not be implied merely because one party obtains a collateral benefit (such as a GST input tax credit); the term must be necessary for the reasonable or effective operation of the contract.
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