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 x_15 is an astronaut if and only if x_15 is rich. For all x_15, x_15 is rich. For all x_15, x_15 will go running. For all x_15, if x_15 goes running, then x_15 is working.
For all x_15, x_15 will work can be inferred via the universal modus ponens rule. For all x_15, x_15 is rich and x_15 will go running can be inferred via the universal conjunction rule. For all x_15, x_15 will go running and x_15 is rich can be inferred via the universal conjunction rule. There is at least one x_15 for which if x_15 were an astronaut, then x_15 is rich can be inferred via the existential biconditional elimination rule. There is at least one x_15 for which if x_15 were rich, then x_15 is an astronaut can be inferred via the existential biconditional elimination rule.