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 for which z is a sailor if and only if z is a writer. For all z, z is a sailor or z is not a nurse.
For all z, if z were a nurse, then z is a sailor can be inferred via the universal rewriting rule. There is at least one z for which if z were a sailor, then z is a writer can be inferred via the existential biconditional elimination rule. There is at least one z for which if z were a writer, then z is a sailor can be inferred via the existential biconditional elimination rule.