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_15, x_15 is an astronaut if and only if x_15 will play tennis. For all x_15, x_15 will make tea. There is at least one x_15 for which x_15 will play tennis.
There is at least one x_15 for which x_15 will play tennis and x_15 will make tea can be inferred via the existential conjunction rule. There is at least one x_15 for which x_15 will make tea and x_15 will play tennis can be inferred via the existential conjunction rule. For all x_15, if x_15 were an astronaut, then x_15 is playing tennis can be inferred via the universal biconditional elimination rule. For all x_15, if x_15 plays tennis, then x_15 is an astronaut can be inferred via the universal biconditional elimination rule.