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, if x_10 were excited, then x_10 is taking a plane. For all x_10, if x_10 writes a letter, then x_10 is drinking water. For all x_10, x_10 will write a letter or x_10 will read a book. For all x_10, if x_10 drinks water, then x_10 is writing a letter. For all x_10, x_10 will drink water if and only if x_10 is excited. For all x_10, x_10 will not take a plane.
For all x_10, x_10 is not excited can be inferred via the universal modus tollens rule. For all x_10, x_10 will write a letter if and only if x_10 will drink water can be inferred via the universal biconditional introduction rule. For all x_10, x_10 will drink water if and only if x_10 will write a letter can be inferred via the universal biconditional introduction rule. For all x_10, if x_10 drinks water, 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 drinking water can be inferred via the universal biconditional elimination rule.