What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Name the inference rule being used: If it is cold, then Mary is sleeping. If Mary sleeps, then it is cold. It is not cold. Mary is sleeping if and only if Jennifer is playing tennis.
Mary is not sleeping can be inferred via the modus tollens rule. It is cold if and only if Mary is sleeping can be inferred via the biconditional introduction rule. Mary is sleeping if and only if it is cold can be inferred via the biconditional introduction rule. If Mary sleeps, then Jennifer is playing tennis can be inferred via the biconditional elimination rule. If Jennifer plays tennis, then Mary is sleeping can be inferred via the biconditional elimination rule.