What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? For all y_4, y_4 is a writer if and only if y_4 is a sailor. For all y_4, y_4 is a writer or y_4 will not take a plane.
For all y_4, if y_4 takes a plane, then y_4 is a writer. For all y_4, if y_4 were a writer, then y_4 is a sailor. For all y_4, if y_4 were a sailor, then y_4 is a writer.