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_5, if x_5 were sad, then x_5 is an office clerk. For all x_5, if x_5 were an office clerk, then x_5 is sad. For all x_5, if x_5 were sad, then x_5 is an office clerk.
For all x_5, x_5 is sad if and only if x_5 is an office clerk can be inferred via the universal biconditional introduction rule. For all x_5, x_5 is an office clerk if and only if x_5 is sad can be inferred via the universal biconditional introduction rule. For all x_5, x_5 is an office clerk if and only if x_5 is sad can be inferred via the universal biconditional introduction rule. For all x_5, x_5 is sad if and only if x_5 is an office clerk can be inferred via the universal biconditional introduction rule.