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: If it is overcast, then Joseph is making tea. For all x_28, x_28 is not a sailor. Joseph is a janitor or it is overcast. William is a nurse if and only if Charles is a sailor. For all x_23, if x_23 were a janitor, then x_23 is making tea.
If William were a nurse, then Charles is a sailor can be inferred via the biconditional elimination rule. If Charles were a sailor, then William is a nurse can be inferred via the biconditional elimination rule.