Consider the following premises. Joseph is fast if and only if Charles is taking a plane. For all y, y will climb a mountain. For all y, if y takes a plane, then y is not climbing a mountain. Can we infer the following from them? Joseph is fast.
 From the fact that for all y, if y takes a plane, then y is not climbing a mountain, and that for all y, y will climb a mountain we can infer that for all y, y will not take a plane. From the fact that for all y, y will not take a plane we can infer that Charles is not taking a plane. From the fact that Joseph is fast if and only if Charles is taking a plane we can infer that if Joseph were fast, then Charles is taking a plane. Finally, from the fact that if Joseph were fast, then Charles is taking a plane, and that Charles is not taking a plane we can infer that Joseph is not fast, which contradicts that Joseph is fast. Therefore, the answer is no.