Consider the following premises. There is at least one x_10 for which x_10 is a sailor if and only if x_10 is a poet. For all x_10, x_10 is a poet if and only if x_10 is a sailor. Can we infer the following from them? If we can, name the inference rule being used: For all x_10, the fact that x_10 were a sailor does not imply that x_10 is a poet.
 From the fact that there is at least one x_10 for which x_10 is a sailor if and only if x_10 is a poet we can infer that there is at least one x_10 for which if x_10 were a sailor, then x_10 is a poet via existential biconditional elimination. Finally, from the fact that for all x_10, x_10 is a poet if and only if x_10 is a sailor we can infer that for all x_10, if x_10 were a poet, then x_10 is a sailor via universal biconditional elimination, which contradicts that For all x_10, the fact that x_10 were a sailor does not imply that x_10 is a poet. Therefore, the answer is no.