Johannes de Villiers Graaff ( also known as Jan de Van Graaff or Jannie Graaff ) ( 19 February 1928 -- 6 January 2015 ) was a neoclassical South African welfare economist .
Johannes de Villiers Graaff ( also known as Jan de Van Graaff or Jannie Graaff ; 19 February 1928 -- 6 January 2015 ) was a South African neoclassical welfare economist .