Consider the following premises. For all x_17, if x_17 climbs a mountain, then x_17 is a mechanic. If Mary were curious, then Joseph is climbing a mountain. Joseph is a mechanic if and only if Mary is curious. Can we infer the following from them? If we can, name the inference rule being used: If Joseph were a mechanic, then Joseph is climbing a mountain.
 From the fact that for all x_17, if x_17 climbs a mountain, then x_17 is a mechanic we can infer that if Joseph climbs a mountain, then Joseph is a mechanic via universal instantiation. From the fact that Joseph is a mechanic if and only if Mary is curious we can infer that if Joseph were a mechanic, then Mary is curious via biconditional elimination. Finally, from the fact that if Joseph were a mechanic, then Mary is curious, and that if Mary were curious, then Joseph is climbing a mountain we can infer that if Joseph were a mechanic, then Joseph is climbing a mountain via transitivity. Therefore, the answer is yes.