In this paper some heuristics for the development of the expert module of an Intelligent Tutoring System are presented: they aim at managing incomplete knowledge and operate in both forward and backward mode. The system generates detailed solutions and the effective user interface allows interacting with the system in a friendly way. In particular, attention is focused on two components of the expert module: namely the module devoted to inference generation (forward module), and the module whose duty is to tackle the problem of managing missing information (missing module).
