Kersten, F. On Understanding Idea and Essence in Husserl and Ingarden: Fred Kersten. The later Husserl and the idea of phenomenology : idealism - realism, historicity and nature ; papers and debate of the International Phenomenological Conference, held at the University of Waterloo, Canada, April 9 - 14, 1969.(1972).

Kersten, Fred. "On Understanding Idea and Essence in Husserl and Ingarden: Fred Kersten." The Later Husserl and the Idea of Phenomenology : Idealism - Realism, Historicity and Nature ; Papers and Debate of the International Phenomenological Conference, Held at the University of Waterloo, Canada, April 9 - 14, 1969.(1972) .

Kersten, Fred. "On Understanding Idea and Essence in Husserl and Ingarden: Fred Kersten." The Later Husserl and the Idea of Phenomenology : Idealism - Realism, Historicity and Nature ; Papers and Debate of the International Phenomenological Conference, Held at the University of Waterloo, Canada, April 9 - 14, 1969.(1972), .