In considering the effect of the two letters it is important to bear in mind two things. In the first place, the appellant's letter purports to give an "option". In other words, it purports to be an offer capable of being accepted so as to create a contract. Moreover, the "option" is given for value, with the obvious intention that it shall not be revocable during the seven days. It follows that, if two constructions of the letter are fairly open, the one of which will make it an effective offer while the other will not, the former construction must be adopted. In the second place, while the due course of completion of a contract for the sale of land is a matter of some complexity, involving the doing of a number of things by both parties, it is very well settled that an informal or "open" contract, not dealing expressly with any of these matters of detail, may be made and be binding. In such a case law and equity fill in the details, so to speak, providing by way of implication for whatever is necessary to effectuate due performance. See generally Williams, Vendor and Purchaser, 4th ed. (1936), pp. 44 et seq. The first step, generally speaking, is for the vendor to show a good title, a comparatively simple matter when the land is under the Torrens system. He must produce his title and answer any requisitions lawfully made upon it. If and when a good title is shown, the purchaser must accept it. After acceptance of title, the purchase money must be paid in exchange for a conveyance, and possession must be given and taken. No time, of course, is fixed for the doing of any of these things. Each step must be taken within a reasonable time, and what is a reasonable time is a question of fact depending on the circumstances of each particular case.