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: For all x_9, x_9 is a janitor. Barbara is not a nurse. Richard is making tea if and only if Barbara is a nurse.
If Richard makes tea, then Barbara is a nurse can be inferred via the biconditional elimination rule. If Barbara were a nurse, then Richard is making tea can be inferred via the biconditional elimination rule. Richard is not making tea can be inferred via the biconditional elimination rule.