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_13, if x_13 were sad, then x_13 is excited. For all x_13, if x_13 sleeps, then x_13 is an office clerk. For all x_13, x_13 will read a book if and only if x_13 is an office clerk. For all x_13, if x_13 were excited, then x_13 is sleeping. For all x_13, x_13 is sad.
For all x_13, x_13 is excited can be inferred via the universal modus ponens rule. For all x_13, if x_13 were sad, then x_13 is sleeping can be inferred via the universal transitivity rule. For all x_13, if x_13 were excited, then x_13 is an office clerk can be inferred via the universal transitivity rule. For all x_13, if x_13 reads a book, then x_13 is an office clerk can be inferred via the universal biconditional elimination rule. For all x_13, if x_13 were an office clerk, then x_13 is reading a book can be inferred via the universal biconditional elimination rule.