Consider the following premises. For all z, z is bored if and only if z is sad. For all z, z is bored if and only if z is sad. Can we infer the following from them? If we can, name the inference rule being used: If John were bored, then John is sad.
 From the fact that for all z, z is bored if and only if z is sad we can infer that for all z, if z were sad, then z is bored via universal biconditional elimination. From the fact that for all z, z is bored if and only if z is sad we can infer that for all z, if z were bored, then z is sad via universal biconditional elimination. From the fact that for all z, if z were bored, then z is sad, and that for all z, if z were sad, then z is bored we can infer that for all z, z is bored if and only if z is sad via universal biconditional introduction. From the fact that for all z, z is bored if and only if z is sad we can infer that John is bored if and only if John is sad via universal instantiation. Finally, from the fact that John is bored if and only if John is sad we can infer that if John were bored, then John is sad via biconditional elimination. Therefore, the answer is yes.