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_3, y_3 is a server or y_3 will not write a letter. For all y_3, y_3 will write a letter if and only if y_3 is a server.
For all y_3, if y_3 writes a letter, then y_3 is a server can be inferred via the universal rewriting rule. For all y_3, if y_3 writes a letter, then y_3 is a server can be inferred via the universal biconditional elimination rule. For all y_3, if y_3 were a server, then y_3 is writing a letter can be inferred via the universal biconditional elimination rule.