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: Richard is a taxi driver if and only if Jessica is running. Jessica is running. Mary is a doctor.
Jessica is running and Mary is a doctor can be inferred via the conjunction rule. Mary is a doctor and Jessica is running can be inferred via the conjunction rule. If Richard were a taxi driver, then Jessica is running can be inferred via the biconditional elimination rule. If Jessica goes running, then Richard is a taxi driver can be inferred via the biconditional elimination rule.