Heddens, J., Speer, W. Today's mathematics: Concepts and methods in elementary school mathematics. New York etc.: Macmillan, 1988 677 p. 0-02-352931-8.
Heddens, J., Speer, W. Today's mathematics: Concepts and methods in elementary school mathematics. New York etc.: Macmillan, 1988 677 p. 0-02-352931-8.
Heddens, J., Speer, W. (1988) Today's mathematics: Concepts and methods in elementary school mathematics, New York etc.: Macmillan 677 p. 0-02-352931-8.
Heddens, J., & Speer, W. (1988). Today's mathematics: Concepts and methods in elementary school mathematics. New York etc.: Macmillan, 677 p.
Heddens J, Speer W. Today's mathematics: Concepts and methods in elementary school mathematics. New York etc.: Macmillan; 1988. p. 677 p. ISBN: 0-02-352931-8.