Consider the following premises. For all y, if y plays squash, then y is climbing a mountain. For all y, y will climb a mountain if and only if y will play squash. There is at least one y for which if y plays squash, then y is climbing a mountain. Can we infer the following from them? For all y, y will climb a mountain if and only if y will play squash.
That is one of the premises. Therefore, the answer is yes.