The aim of our work is to investigate how a relatively small set of clauses can be transformed into a running program capable of solving a number of problems. The problems are chosen from the domain of simple arithmetic, algebra and letter series completion. We describe how the problems are solved, how errors are detected and corrected by modification of the existing clauses. Various techniques useful in the process of error detection and correction are described in detail. Two types of errors are dealt with: selection errors arising due to incorrect selection of clauses, and instantiation errors arising when the partial results (subgoals) are not specific enough. The system described was implemented in Prolog.