When Yang Luchan arrived in Beijing, he taught 10 taiji sets at the mansion of Prince Duan. These 10 sets form a complete taiji syllabus. Whilst teaching at the mansion, Yang accepted two disciples: one was Wang Lanting (whose teachings form the basis of Li [Ruidong] style taiji), the other was Fu Zhou. Both of these people were men of rank within the mansion: Wang Lanting was Prince Duan’s housekeeper, in modern terms he was responsible for the security of the House; Fu Zhou was a Manchu general with a very solid foundation in martial arts. Both of these men only became Yang Luchan’s disciples after losing to him in several challenges. And so Yang taught them these 10 original sets of Yang style taiji..............

L: After I’d basically mastered Fu Nei Pai, I wanted to be able to compare and analyse the public 85 set against what I’d learnt, and so during 1990-1991 I went to Xi’an to find M Zhao Bin. I chose M Zhao thinking that, because he was a relative of Yang Chengfu’s (ed. specifically, Zhao Bin was the son of Yang Cong, the daughter of Yang Jianhou’s second son, Yang Zhaoyuan, making him Chengfu’s grand-nephew), his form would be orthodox.

After I had learnt the 85 set, I could see traces of the original sets I had learnt from M Zhai in the 85. Actually, a lot of the hand techniques [shoufa] and body requirements [shenfa] of Wu style, Hao style and Sun style all preserve traces of early Yang style as passed down to us in Fu Nei Pai.

A: Just now, you mentioned that there are 10 sets in Fu Nei Pai taiji. Could you describe each one briefly?

L: The 10 sets are (in order):

1: Zhi Chui (Wisdom fist)

2: Large frame

3: Old frame (also called the Middle Frame)

4: Small Frame

5: Xiao Jiu Tian (Nine Little Heavens)

6: Hou Tian Fa (Post-Heaven Methods)

7: 30-posture Sanshou

8: Taiji Chang Quan (Long Boxing)

9: Shi San Dan Gongfa (lit. 13 cinnabar methods; in Taoist alchemy, it was thought that the elixir of immortality could be produced from cinnabar)

10. Taiji Dian Xue (striking vital points)

These ten sets form a gradated series of practice, from lower to higher levels, from external to internal.

Full article - https://wulinmingshi.wordpress.com/2009/01/30/fu-nei-pai-taiji-of-li-zheng/