* Walter Rudin, "Principles of Mathematical Analysis", 3rd Edition, Chapter 2, exercise 27* John C. Oxtoby, "Measure and Category", 2nd Edition (1980),
==References==* Walter Rudin, "Principles of Mathematical Analysis", 3rd Edition, Chapter 2, exercise 27* John C. Oxtoby, "Measure and Category", 2nd Edition (1980),* Lynn Steen and J. Arthur Seebach, Jr., "Counterexamples in Topology", 2nd Edition, pg.