I strongly agree what 小麥 said. He isnt good at this field. Actually, I read what he post on the internet years ago. I found something points which is too redicious. like 2 and 3, he suggest use 5 to solve. it will just get in worse off. wont get it any better. it should depends on what's ppl's number, and use different solution. cannot strictly say 5 is the key and 5 in natural. no 5 in real at all. you cant tell what's the real 5, what if it's 2. then what. worse and worser??

He book is just condensation of what he read from the other old books and i can tell he mis-read some. so dont take all. worth to read in the way as false case.

Allen