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, x_13 will take a plane or x_13 will drink water. For all x_13, if x_13 drinks water, then x_13 is reading a book. There is at least one x_13 for which x_13 will take a plane if and only if x_13 will read a book.
There is at least one x_13 for which if x_13 takes a plane, then x_13 is reading a book can be inferred via the existential biconditional elimination rule. There is at least one x_13 for which if x_13 reads a book, then x_13 is taking a plane can be inferred via the existential biconditional elimination rule.