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_7, x_7 will write a letter if and only if x_7 will cook. For all x_7, x_7 will not write a letter. For all x_7, x_7 will cook or x_7 will read a book.
For all x_7, if x_7 writes a letter, then x_7 is cooking can be inferred via the universal biconditional elimination rule. For all x_7, if x_7 cooks, then x_7 is writing a letter can be inferred via the universal biconditional elimination rule. For all x_7, x_7 will not cook can be inferred via the universal biconditional elimination rule.