Consider the following premises. For all x_2, x_2 is a mechanic if and only if x_2 is an office clerk. Can we infer the following from them? If we can, name the inference rule being used: The fact that Thomas were a mechanic does not imply that Thomas is an office clerk.
 From the fact that for all x_2, x_2 is a mechanic if and only if x_2 is an office clerk we can infer that Thomas is a mechanic if and only if Thomas is an office clerk via universal instantiation. Finally, from the fact that Thomas is a mechanic if and only if Thomas is an office clerk we can infer that if Thomas were a mechanic, then Thomas is an office clerk via biconditional elimination, which contradicts that The fact that Thomas were a mechanic does not imply that Thomas is an office clerk. Therefore, the answer is no.