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_6 for which if x_6 were curious, then x_6 is taking a plane. For all x_6, if x_6 takes a plane, then x_6 is curious. For all x_6, if x_6 plays tennis, then x_6 is taking a plane. For all x_6, x_6 will play tennis or x_6 is curious.
For all x_6, if x_6 plays tennis, then x_6 is curious can be inferred via the universal transitivity rule. There is at least one x_6 for which x_6 will take a plane can be inferred via the existential disjunction elimination rule. There is at least one x_6 for which x_6 is curious if and only if x_6 will take a plane can be inferred via the existential biconditional introduction rule. There is at least one x_6 for which x_6 will take a plane if and only if x_6 is curious can be inferred via the existential biconditional introduction rule.