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 z_1 for which if z_1 makes tea, then z_1 is rich. For all z_1, if z_1 were rich, then z_1 is making tea. For all z_1, if z_1 makes tea, then z_1 is rich.
For all z_1, z_1 is rich if and only if z_1 will make tea can be inferred via the universal biconditional introduction rule. For all z_1, z_1 will make tea if and only if z_1 is rich can be inferred via the universal biconditional introduction rule. There is at least one z_1 for which z_1 will make tea if and only if z_1 is rich can be inferred via the existential biconditional introduction rule. There is at least one z_1 for which z_1 is rich if and only if z_1 will make tea can be inferred via the existential biconditional introduction rule.