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: It is overcast. For all y_1, y_1 is fast if and only if y_1 is a nurse. If Barbara were fast, then it is not overcast.
Barbara is not fast can be inferred via the modus tollens rule. For all y_1, if y_1 were fast, then y_1 is a nurse can be inferred via the universal biconditional elimination rule. For all y_1, if y_1 were a nurse, then y_1 is fast can be inferred via the universal biconditional elimination rule.