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_3 for which if x_3 were happy, then x_3 is a soldier. For all x_3, if x_3 were a soldier, then x_3 is happy. For all x_3, if x_3 were happy, then x_3 is a soldier.
For all x_3, x_3 is a soldier if and only if x_3 is happy can be inferred via the universal biconditional introduction rule. For all x_3, x_3 is happy if and only if x_3 is a soldier can be inferred via the universal biconditional introduction rule. There is at least one x_3 for which x_3 is happy if and only if x_3 is a soldier can be inferred via the existential biconditional introduction rule. There is at least one x_3 for which x_3 is a soldier if and only if x_3 is happy can be inferred via the existential biconditional introduction rule.