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_4 for which z_4 will not drink water. For all z_4, z_4 will drink water if and only if z_4 is a taxi driver. For all z_4, if z_4 were a taxi driver, then z_4 is drinking water.
There is at least one z_4 for which z_4 is not a taxi driver can be inferred via the existential modus tollens rule. For all z_4, if z_4 drinks water, then z_4 is a taxi driver can be inferred via the universal biconditional elimination rule. For all z_4, if z_4 were a taxi driver, then z_4 is drinking water can be inferred via the universal biconditional elimination rule. There is at least one z_4 for which z_4 is not a taxi driver can be inferred via the existential biconditional elimination rule.