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_13 for which x_13 is fast if and only if x_13 is an office clerk. For all x_13, x_13 will read a book if and only if x_13 is fast. For all x_13, if x_13 reads a book, then x_13 is taking a plane. For all x_13, x_13 will not take a plane.
For all x_13, x_13 will not read a book can be inferred via the universal modus tollens rule. For all x_13, if x_13 reads a book, then x_13 is fast can be inferred via the universal biconditional elimination rule. There is at least one x_13 for which if x_13 were fast, then x_13 is an office clerk can be inferred via the existential biconditional elimination rule. For all x_13, if x_13 were fast, then x_13 is reading a book can be inferred via the universal biconditional elimination rule. There is at least one x_13 for which if x_13 were an office clerk, then x_13 is fast can be inferred via the existential biconditional elimination rule.