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 y, if y makes tea, then y is working. Richard is not making tea. For all y, if y works, then y is making tea. Richard is a cashier.
Richard is not making tea and Richard is a cashier can be inferred via the conjunction rule. Richard is a cashier and Richard is not making tea can be inferred via the conjunction rule. For all y, y will make tea if and only if y will work can be inferred via the universal biconditional introduction rule. For all y, y will work if and only if y will make tea can be inferred via the universal biconditional introduction rule.