10. In a 20-year lease contract over a building, the lessee is expressly granted a right of first refusal should the lessor decide to sell both the land and the building. However, the lessor sold the property to a third person who knew about the lease and in fact agreed to respect it. Consequently the lessee brought an action against both the lessor-seller and the third party-buyer (a) to rescind the sale of the property in favor of the third party-buyer and (b) to compel specific performance of his right of first refusal in the sense that the lessor should be ordered by the court to execute a deed of absolute sale in favor of the lessee. The defendants contend that the plaintiff can neither seek rescission of the sale nor compel specific performance of a "mere" right of first refusal. Decide the case with reasons.