Consider the following premises. Charles is not playing squash. It is sunny if and only if Joseph is drinking water. Charles is an office clerk if and only if it is sunny. For all x_12, x_12 is an office clerk if and only if x_12 will play squash. Can we infer the following from them? If we can, name the inference rule being used: Joseph is not drinking water.
 From the fact that for all x_12, x_12 is an office clerk if and only if x_12 will play squash we can infer that Charles is an office clerk if and only if Charles is playing squash via universal instantiation. From the fact that Charles is an office clerk if and only if Charles is playing squash, and that Charles is not playing squash we can infer that Charles is not an office clerk via biconditional elimination. From the fact that Charles is an office clerk if and only if it is sunny, and that Charles is not an office clerk we can infer that it is not sunny via biconditional elimination. Finally, from the fact that it is sunny if and only if Joseph is drinking water, and that it is not sunny we can infer that Joseph is not drinking water via biconditional elimination. Therefore, the answer is yes.