@book{254,
	author = {Ginsburg, Herbert. and Opper, Sylvia,},
	title = {Piaget's theory of intellectual development :},
	publisher = {Prentice-Hall,},
	year = {[1969] },
	series = {The Prentice-Hall series in developmental psychology},
	address = {Englewood Cliffs, N.J. :}
}