Pietersma, H. The Concept of Horizon: H. Pietersma. 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).

Pietersma, H. "The Concept of Horizon: H. Pietersma." 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) .

Pietersma, H. "The Concept of Horizon: H. Pietersma." 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), .