[1]The Symbolic Concept Acquisition version 2 model by Pearson (based on Miller's work) and the Subtraction model by Jones (based on Brown and VanLehn's work) from the University of Michigan are nice exceptions that also inspired this work. They include explanatory displays and their code is available. They (or their authors) are available through http://ai.eecs.umich.edu/soar/soar-group.html.