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_8, if x_8 were a server, then x_8 is playing tennis. For all x_8, if x_8 were a server, then x_8 is playing tennis. For all x_8, if x_8 plays tennis, then x_8 is a server.
For all x_8, x_8 is a server if and only if x_8 will play tennis can be inferred via the universal biconditional introduction rule. For all x_8, x_8 is a server if and only if x_8 will play tennis can be inferred via the universal biconditional introduction rule. For all x_8, x_8 will play tennis if and only if x_8 is a server can be inferred via the universal biconditional introduction rule. For all x_8, x_8 will play tennis if and only if x_8 is a server can be inferred via the universal biconditional introduction rule.