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, if x_9 were a sailor, then x_9 is climbing a mountain. For all x_9, if x_9 climbs a mountain, then x_9 is a sailor. For all x_9, x_9 will climb a mountain if and only if x_9 is a scientist. There is at least one x_9 for which x_9 is not a scientist.
For all x_9, x_9 is a sailor if and only if x_9 will climb a mountain can be inferred via the universal biconditional introduction rule. For all x_9, x_9 will climb a mountain if and only if x_9 is a sailor can be inferred via the universal biconditional introduction rule. For all x_9, if x_9 climbs a mountain, then x_9 is a scientist can be inferred via the universal biconditional elimination rule. For all x_9, if x_9 were a scientist, then x_9 is climbing a mountain can be inferred via the universal biconditional elimination rule. There is at least one x_9 for which x_9 will not climb a mountain can be inferred via the existential biconditional elimination rule.