Consider the following premises. Michael is writing a letter. For all x_11, x_11 will drive a car if and only if x_11 will climb a mountain. Susan is not driving a car. Can we infer the following from them? If we can, name the inference rule being used: Susan is climbing a mountain.
 From the fact that for all x_11, x_11 will drive a car if and only if x_11 will climb a mountain we can infer that Susan is driving a car if and only if Susan is climbing a mountain via universal instantiation. Finally, from the fact that Susan is driving a car if and only if Susan is climbing a mountain, and that Susan is not driving a car we can infer that Susan is not climbing a mountain via biconditional elimination, which contradicts that Susan is climbing a mountain. Therefore, the answer is no.