I found the use of multiplication particularly useful, since it forced the reader to pay attention to the physical/logical distinction. If, say, addition had been used, then a determined reader could try to use physical constraints alone (though they would be cheating).
I found the use of multiplication particularly useful, since it forced the reader to pay attention to the physical/logical distinction. If, say, addition had been used, then a determined reader could try to use physical constraints alone (though they would be cheating).