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: William is playing tennis. William is playing tennis if and only if Joseph is a janitor. If Thomas drinks water, then Joseph is not a janitor.
If William plays tennis, then Joseph is a janitor can be inferred via the biconditional elimination rule. If Joseph were a janitor, then William is playing tennis can be inferred via the biconditional elimination rule.