Mitsui & Co. (Canada) Ltd. v. Royal Bank of Canada, [1995] 2 SCR 187 -- summary under Subsection 49(3)

Major J. noted, with respect to a clause in a lease that gave the lessee the unilateral right to compel the lessor to sell helicopters to the lessee at their reasonable fair market value, that the giving of initial notice by the lessee 120 days prior to the expiry of the lease could not qualify as an "exercise" of the option (irrespective of how the giving of notice was labelled), given that the exercise of an option must lead to a binding contract of a purchase and sale. Instead, the determination by the lessor of the reasonable fair market value of the helicopters, along with the giving of the initial notice, were conditions precedent to the exercise of the option. Accordingly, "the option could only be exercised by the lessee giving its written assent to the valuation performed by the lessor" (p. 202).