[rgarlikov]

This was about one lesson, and yes that lesson needs reinforcement. But part of that was being done by those students who were inspired to try it with other mathematical "bases", such as base 3 -- a system with 3 digits. Also, in a full course, if you consistently and frequently use the Socratic method or any method that questions students' logic, many of them begin to do that on their own about their logic or, usually, the logic of other people, even the teacher. I have had students come up with good flaws in my own logic, by the middle or end of the term. But yes, it takes reinforcement.