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, if y were rich, then y is poor. There is at least one y for which if y were poor, then y is rich. For all y, y is not rich.
There is at least one y for which y is not poor can be inferred via the existential modus tollens rule. There is at least one y for which y is poor if and only if y is rich can be inferred via the existential biconditional introduction rule. There is at least one y for which y is rich if and only if y is poor can be inferred via the existential biconditional introduction rule.