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 y_1, if y_1 were poor, then y_1 is playing tennis. There is at least one y_1 for which if y_1 plays tennis, then y_1 is poor.
There is at least one y_1 for which y_1 will play tennis if and only if y_1 is poor can be inferred via the existential biconditional introduction rule. There is at least one y_1 for which y_1 is poor if and only if y_1 will play tennis can be inferred via the existential biconditional introduction rule.