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_10, x_10 is not a nurse. John is a nurse if and only if David is happy.
If John were a nurse, then David is happy can be inferred via the biconditional elimination rule. If David were happy, then John is a nurse can be inferred via the biconditional elimination rule.