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_9, if x_9 cooks, then x_9 is reading a book. For all x_9, if x_9 reads a book, then x_9 is cooking. For all x_9, x_9 will read a book or x_9 will play tennis. For all x_9, x_9 will cook if and only if x_9 will play tennis.
For all x_9, x_9 will cook if and only if x_9 will read a book can be inferred via the universal biconditional introduction rule. For all x_9, x_9 will read a book if and only if x_9 will cook can be inferred via the universal biconditional introduction rule. For all x_9, if x_9 cooks, then x_9 is playing tennis can be inferred via the universal biconditional elimination rule. For all x_9, if x_9 plays tennis, then x_9 is cooking can be inferred via the universal biconditional elimination rule.