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 y_1, y_1 will write a letter if and only if y_1 will read a book. For all y_1, y_1 will not write a letter. William is reading a book or it is cold.
For all y_1, if y_1 writes a letter, then y_1 is reading a book can be inferred via the universal biconditional elimination rule. For all y_1, if y_1 reads a book, then y_1 is writing a letter can be inferred via the universal biconditional elimination rule. For all y_1, y_1 will not read a book can be inferred via the universal biconditional elimination rule.