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: There is at least one x_3 for which x_3 will write a letter or x_3 will read a book. For all x_3, x_3 will write a letter if and only if x_3 is a poet. For all x_3, if x_3 reads a book, then x_3 is a poet.
For all x_3, if x_3 writes a letter, then x_3 is a poet can be inferred via the universal biconditional elimination rule. For all x_3, if x_3 were a poet, then x_3 is writing a letter can be inferred via the universal biconditional elimination rule.