7Gravemeijer K, Terwel J. Hans Freudenthal: a Mathematician on Didactics and Curriculum Theory [J]. Journal of Curriculum Studies, 2000, 32(6): 777-796.
8Freudenthal H. Mathematics as an Educational Task [M]. Dordrecht, The Netherlands: Reidel, 1973.
9Freudenthal H. Geometry between the Devil and the Deep Sea [J]. Educational Studies in Mathematics, 1971, 3(3-4):413-435.