Consider the following premises. If Elisabeth were a poet, then David is a lawyer. Elisabeth is a poet if and only if David is a lawyer. Can we infer the following from them? If we can, name the inference rule being used: David is a lawyer if and only if Elisabeth is a poet.
 From the fact that Elisabeth is a poet if and only if David is a lawyer we can infer that if David were a lawyer, then Elisabeth is a poet via biconditional elimination. Finally, from the fact that if David were a lawyer, then Elisabeth is a poet, and that if Elisabeth were a poet, then David is a lawyer we can infer that David is a lawyer if and only if Elisabeth is a poet via biconditional introduction. Therefore, the answer is yes.