Linear syntax for communicating elementary mathematics

We consider computer aided assessment (CAA) of mathematics in which a student provides an answer in the form of a mathematical expression. A common approach is for CAA system implementors to adopt a linear syntax to allow students to communicate their answer to the machine. In this paper we consider the problems students encounter when mediating between (i) traditional mathematical notation and (ii) the requirements of a strict computer algebra system (CAS) syntax. We compare the linear syntaxes of five commonly used general purpose CAS, and report surprising variety even at the elementary levels.