Consider the following premises. Jessica is an office clerk or Charles is not sad. If Charles were sad, then Jessica is an office clerk. If Jessica were an office clerk, then Charles is sad. Can we infer the following from them? If we can, name the inference rule being used: If is not true that Jessica is an office clerk if and only if Charles is sad.
 From the fact that Jessica is an office clerk or Charles is not sad we can infer that if Charles were sad, then Jessica is an office clerk via rewriting. Finally, from the fact that if Jessica were an office clerk, then Charles is sad, and that if Charles were sad, then Jessica is an office clerk we can infer that Jessica is an office clerk if and only if Charles is sad via biconditional introduction, which contradicts that If is not true that Jessica is an office clerk if and only if Charles is sad. Therefore, the answer is no.