@conference {678587,
	title = {On the Nature and Origin of Algebraic Symbolism},
	booktitle = {New Perspectives on Mathematical Practices. Essays in Philosophy and History of Mathematics.},
	year = {2009},
	publisher = {World Scientific Publishing},
	organization = {World Scientific Publishing},
	isbn = {978-981-281-222-3},
	url = {http://www.worldscibooks.com/etextbook/6810/6810\_chap01.pdf},
	author = {Heeffer, Albrecht},
	editor = {Van Kerkhove, Bart}
}
@conference {428001,
	title = {Negative numbers as an epistemic difficult concept. Some lessons from history.},
	booktitle = {History and Pedagogy of Mathematics. Satellite Meeting of International Congress on Mathematical Education 11, 14 - 18 July 2008.},
	year = {2008},
	publisher = {Centro Cultural del M{\'e}xico Contemporan{\'e}o},
	organization = {Centro Cultural del M{\'e}xico Contemporan{\'e}o},
	abstract = {<p>Historical studies on the development of mathematical concepts will serve mathematics teachers to relate their students difficulties in understanding to conceptual problems in the history of mathematics. We argue that one popular tool for teaching about numbers, the number line, may not be fit for early teaching of operations involving negative numbers. Our arguments are drawn from the many discussions on negative numbers during the seventeenth and eighteenth centuries from philosophers and mathematicians as Arnauld, Leibniz, Wallis, Euler and dAlembert. Not only the division by negative numbers poses problems for the number line, but also the very idea of quantities smaller than nothing has been challenged. Drawing lessons from the history of mathematics we argue for the introduction of negative numbers in education within the context of symbolic operations.</p>},
	author = {Heeffer, Albrecht},
	editor = {Tzanakis, C.}
}
@booklet {heeffer2007near,
	title = {Near-optimal strategies for the game of Logik},
	year = {2007},
	abstract = {<p>Logik is an interesting variation of the game of Mastermind. For the latter several strategies have been proposed. We present some computational results for existing and new strategies applied to Logik. Our results give some indication on the scalability and applicability of these strategies to similar games.</p>},
	author = {Heeffer, Albrecht and Heeffer, Harold}
}
