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 making tea or it is late. For all y, y is not a janitor. John is playing tennis if and only if David is a janitor. For all x_23, if x_23 makes tea, then x_23 is playing squash. If it is late, then Richard is playing squash.
If John plays tennis, then David is a janitor can be inferred via the biconditional elimination rule. If David were a janitor, then John is playing tennis can be inferred via the biconditional elimination rule.