The fist number of L. refer to the standard CtP edition published in 1987. The following number shows correspondence between letters in the new 2010 edition. Note that on this website CtP is available only 1987 edition with minor additions.

[L. 51 | 58] 29 May 1963

As regards my views on the Abhidhamma Pitaka, for my general attitude see Preface (a). More particularly, I consider that none of the A.P. is the Buddha's word, and furthermore, that it is a positively misleading compilation, often inconsistent with the Suttas. This does not mean, however, that I regard every single statement in it as false—the short work, the Puggala Paññatti, may well be trustworthy in parts. But I must confess that most of my acquaintance with the A.P. is at second hand. I have never, myself, found anything in it of the slightest value to me, and I normally advise people to leave it entirely alone. If you press me, I might express myself more emphatically on the uselessness and misleadingness of the A.P., but since I do not think you are violently enamoured of it, perhaps I have said enough.