Fred Richman Omniscience Principles and Functions of Bounded Variation. 111-116 2002 48 Math. Log. Q. 1 http://dx.doi.org/10.1002/1521-3870(200201)48:1<111::AID-MALQ111>3.0.CO;2-6 db/journals/mlq/mlq48.html#Richman02