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: There is at least one x_15 for which if x_15 drives a car, then x_15 is a scientist. For all x_15, if x_15 were a taxi driver, then x_15 is climbing a mountain. For all x_15, if x_15 climbs a mountain, then x_15 is driving a car. For all x_15, x_15 is a scientist if and only if x_15 is a taxi driver.
For all x_15, if x_15 were a taxi driver, then x_15 is driving a car can be inferred via the universal transitivity rule. There is at least one x_15 for which if x_15 climbs a mountain, then x_15 is a scientist can be inferred via the existential transitivity rule. For all x_15, if x_15 were a scientist, then x_15 is a taxi driver can be inferred via the universal biconditional elimination rule. For all x_15, if x_15 were a taxi driver, then x_15 is a scientist can be inferred via the universal biconditional elimination rule.