Vol. 11 Num. 1 (1991) Paul Dowling Gender, class, and subjectivity in mathematics: a critique of Humpty Dumpty2 Avery Solomon What is a line?9 Michèle Artigue , Marie-Jean Perrin-Glorian Didactic engineering, research and development tool: some theoretical problems linked to this duality13 Anna Sfard The case of the vanishing tuples19 Lisa Hefendehl-Hebeker Negative numbers: obstacles in their evolution from intuitive to intellectual constructs26 Barry Onslow Linking reality and symbolism: a primary function of mathematics education33 Guershon Harel , David Tall The general, the abstract, and the generic in advanced mathematics38 Martha B. Burton Grammatical translation-inhibitors in two classic word problem sentences43