Consider the following premises. For all x, x is happy if and only if x is curious. There is at least one x for which if x were an office clerk, then x is happy. For all x, x is an office clerk. Can we infer the following from them? If we can, name the inference rule being used: For all x, x is not curious.
 From the fact that there is at least one x for which if x were an office clerk, then x is happy, and that for all x, x is an office clerk we can infer that there is at least one x for which x is happy via existential modus ponens. From the fact that for all x, x is happy if and only if x is curious we can infer that for all x, if x were happy, then x is curious via universal biconditional elimination. Finally, from the fact that for all x, if x were happy, then x is curious, and that there is at least one x for which x is happy we can infer that there is at least one x for which x is curious via existential modus ponens, which contradicts that For all x, x is not curious. Therefore, the answer is no.