How did the scale in the proof of question 20 in Tianjin 20 14 college entrance examination mathematics text come from?
Both ai and bi come from the set m, and they are both non-negative, so ai-bi is the subtraction of two non-negative numbers. The largest difference is ai, and the largest number ai can get is q- 1, that is, ai-bi≤q- 1. So all ai-bi numbers are converted into q- 1.