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_6, if x_6 were happy, then x_6 is driving a car. There is at least one x_6 for which if x_6 climbs a mountain, then x_6 is happy. For all x_6, x_6 will not drive a car. For all x_6, if x_6 were happy, then x_6 is climbing a mountain.
For all x_6, x_6 is not happy can be inferred via the universal modus tollens rule. There is at least one x_6 for which if x_6 climbs a mountain, then x_6 is driving a car can be inferred via the existential transitivity rule. There is at least one x_6 for which x_6 will climb a mountain if and only if x_6 is happy can be inferred via the existential biconditional introduction rule. There is at least one x_6 for which x_6 is happy if and only if x_6 will climb a mountain can be inferred via the existential biconditional introduction rule.