Stunted varieties were generally chosen, particularly if they had the side branches opposite or regular, for much depends upon this; a one-sided tree is of no value in the eyes of the Chinese. ↗
There's a boom in genealogy now. With ancestry.com and other sites digitizing so many of the records, you can now find things in a few minutes that used to take months. ↗
The problem of distinguishing prime numbers from composite numbers and of resolving the latter into their prime factors is known to be one of the most important and useful in arithmetic. ↗