The binding legal principles established are: (1) For rei vindicatio to succeed, the applicant must prove ownership of the property, the respondent's possession thereof, and the absence of lawful basis for that possession. Where a sale agreement is validly cancelled due to the purchaser's breach, the purchaser has no lawful basis to retain the title deeds. (2) The doctrine of fictional fulfilment (that a condition is deemed fulfilled against a person who has designedly prevented its fulfilment) only operates during the life span of the agreement and within the contractual time frames specified therein. (3) Where a contract specifies a fixed date for performance, the principle dies interpellat pro homine applies: the creditor need make no demand, and the debtor is in mora if he fails to perform on the appointed date. (4) Specific performance is a discretionary remedy that should be refused where it would produce an unjust result or operate unduly harshly on one party. In circumstances of currency devaluation and hyperinflation, specific performance will be refused where it would enable a party to acquire valuable property for a nominal sum that bears no relation to its actual value. (5) A party alleging trade usage must prove that it is universally and uniformly observed, long-established, notorious, reasonable, certain, and does not conflict with positive law or the clear provisions of the contract.