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_4, y_4 is an astronaut. If John were an office clerk, then John is not an astronaut. Richard is a lawyer if and only if John is not an office clerk.
If Richard were a lawyer, then John is not an office clerk can be inferred via the biconditional elimination rule. If John were not an office clerk, then Richard is a lawyer can be inferred via the biconditional elimination rule.