It doesn't seem efficient, or very useful to aid understanding. It replaces one operation by many operations. It trades one abstraction by increasing the memor

It doesn't seem efficient, or very useful to aid understanding. It replaces one operation by many operations. It trades one abstraction by increasing the memory requirements (external memory, in the paper). At least I had finished the subtraction in my head way before I was reading halfway through the 'new' method, in all examples. It would be useful if they students could each design their own favourite subtraction algorithm, and compare notes with fellow students, instead of having to memorize 3 or 4 cookie cutter algorithms.