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_9 for which x_9 will not play squash. For all x_9, x_9 will play squash if and only if x_9 will play tennis. For all x_9, if x_9 were a doctor, then x_9 is making tea. For all x_9, if x_9 makes tea, then x_9 is playing tennis.
For all x_9, if x_9 were a doctor, then x_9 is playing tennis can be inferred via the universal transitivity rule. For all x_9, if x_9 plays squash, then x_9 is playing tennis can be inferred via the universal biconditional elimination rule. For all x_9, if x_9 plays tennis, then x_9 is playing squash can be inferred via the universal biconditional elimination rule. There is at least one x_9 for which x_9 will not play tennis can be inferred via the existential biconditional elimination rule.