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: Robert is not a janitor. Robert is a police officer or David is listening to a song. Robert is a police officer if and only if Robert is a janitor.
If Robert were a police officer, then Robert is a janitor can be inferred via the biconditional elimination rule. If Robert were a janitor, then Robert is a police officer can be inferred via the biconditional elimination rule. Robert is not a police officer can be inferred via the biconditional elimination rule.