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: David is an astronaut or it is late. Michael is a janitor if and only if David is an astronaut. Michael is a janitor or it is not late.
If it is late, then Michael is a janitor can be inferred via the rewriting rule. If Michael were a janitor, then David is an astronaut can be inferred via the biconditional elimination rule. If David were an astronaut, then Michael is a janitor can be inferred via the biconditional elimination rule.