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 cold if and only if Barbara is climbing a mountain. For all x_7, if x_7 climbs a mountain, then x_7 is not fast. For all x_7, x_7 is fast.
If it is cold, then Barbara is climbing a mountain can be inferred via the biconditional elimination rule. If Barbara climbs a mountain, then it is cold can be inferred via the biconditional elimination rule. For all x_7, x_7 will not climb a mountain can be inferred via the universal modus tollens rule.