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 x_6, if x_6 were a writer, then x_6 is an electrician. There is at least one x_6 for which x_6 is a sailor if and only if x_6 is a writer. For all x_6, if x_6 were an electrician, then x_6 is a sailor.
For all x_6, if x_6 were a writer, then x_6 is a sailor can be inferred via the universal transitivity rule. There is at least one x_6 for which if x_6 were a sailor, then x_6 is a writer can be inferred via the existential biconditional elimination rule. There is at least one x_6 for which if x_6 were a writer, then x_6 is a sailor can be inferred via the existential biconditional elimination rule.