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_9, x_9 will climb a mountain if and only if x_9 is a sailor. For all x_9, x_9 is not a sailor. For all x_9, if x_9 climbs a mountain, then x_9 is a nurse. For all x_9, if x_9 were a nurse, then x_9 is climbing a mountain.
For all x_9, x_9 will climb a mountain if and only if x_9 is a nurse can be inferred via the universal biconditional introduction rule. For all x_9, x_9 is a nurse if and only if x_9 will climb a mountain can be inferred via the universal biconditional introduction rule. For all x_9, if x_9 climbs a mountain, then x_9 is a sailor can be inferred via the universal biconditional elimination rule. For all x_9, if x_9 were a sailor, then x_9 is climbing a mountain can be inferred via the universal biconditional elimination rule. For all x_9, x_9 will not climb a mountain can be inferred via the universal biconditional elimination rule.