I prefer the simplest solution, saying "OOPS, forget it, I made a mistake. Lets do something else." and returning to teach something much more basic. In this, I follow my teacher, who does not hesitate to act this way even though he is senior.

Well said. And very good advice. I've done exactly that myself. It shows ME that I need to spend some time relearning that technique. And it shows STUDENTS that even a teacher should remember to be humble.

Shannon