Input design in interactive learning environment T-algebra

T-algebra is an interactive learning environment for step-by-step solving of algebra problems. To make the diagnosis of mistakes more complete, each solution step in T-algebra consists of three stages: selection of the transformation rule, marking the parts of expression, entering the result of the operation. This article describes the last stage that can proceed in three different modes: free input, pattern-driven input and input of some components of the result.