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 z_4, if z_4 were a lawyer, then z_4 is an astronaut. For all z_4, z_4 is a lawyer if and only if z_4 is an astronaut. For all z_4, z_4 is not a lawyer.
For all z_4, if z_4 were a lawyer, then z_4 is an astronaut can be inferred via the universal biconditional elimination rule. For all z_4, if z_4 were an astronaut, then z_4 is a lawyer can be inferred via the universal biconditional elimination rule. For all z_4, z_4 is not an astronaut can be inferred via the universal biconditional elimination rule.