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_10, x_10 will write a letter or x_10 is not a cashier. For all x_10, x_10 is a cashier. For all x_10, x_10 will write a letter if and only if x_10 is excited.
For all x_10, if x_10 were a cashier, then x_10 is writing a letter can be inferred via the universal rewriting rule. For all x_10, if x_10 writes a letter, then x_10 is excited can be inferred via the universal biconditional elimination rule. For all x_10, if x_10 were excited, then x_10 is writing a letter can be inferred via the universal biconditional elimination rule.