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: Elisabeth is a nurse if and only if Thomas is fast. For all x_6, if x_6 were a nurse, then x_6 is a politician. For all x_6, x_6 is not a politician.
If Elisabeth were a nurse, then Thomas is fast can be inferred via the biconditional elimination rule. If Thomas were fast, then Elisabeth is a nurse can be inferred via the biconditional elimination rule. For all x_6, x_6 is not a nurse can be inferred via the universal modus tollens rule.