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_9, if x_9 were curious, then x_9 is excited. There is at least one x_9 for which x_9 will play squash. For all x_9, if x_9 were excited, then x_9 is curious. For all x_9, if x_9 were excited, then x_9 is not playing squash.
There is at least one x_9 for which x_9 is not excited can be inferred via the existential modus tollens rule. For all x_9, x_9 is curious if and only if x_9 is excited can be inferred via the universal biconditional introduction rule. For all x_9, x_9 is excited if and only if x_9 is curious can be inferred via the universal biconditional introduction rule.