Consider the following premises. Michael is playing tennis if and only if John is a sailor. John is not a sailor. Can we infer the following from them? If we can, name the inference rule being used: Michael is playing tennis.
 From the fact that Michael is playing tennis if and only if John is a sailor we can infer that if Michael plays tennis, then John is a sailor via biconditional elimination. Finally, from the fact that if Michael plays tennis, then John is a sailor, and that John is not a sailor we can infer that Michael is not playing tennis via modus tollens, which contradicts that Michael is playing tennis. Therefore, the answer is no.