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 takes a plane, then x_6 is excited. For all x_6, if x_6 were excited, then x_6 is curious. For all x_6, if x_6 were happy, then x_6 is taking a plane. For all x_6, if x_6 were curious, then x_6 is happy.
For all x_6, if x_6 takes a plane, then x_6 is curious can be inferred via the universal transitivity rule. For all x_6, if x_6 were excited, then x_6 is happy can be inferred via the universal transitivity rule. For all x_6, if x_6 were happy, then x_6 is excited can be inferred via the universal transitivity rule. For all x_6, if x_6 were curious, then x_6 is taking a plane can be inferred via the universal transitivity rule.