I'm writing a paper in which I cite a lot of results that appear in Schikhof's *Ultrametric Calculus*. Some of these results are exercises in Schikhof's book. These exercises are not difficult, but are laborious. Thus, if I write the proofs, the article may extend by about two or three pages.


Should I write the proofs or simply cite them? Schikhof is a very well respected mathematician, and I have never found any errors in his book. Obviously, I have checked that the exercises are correct.


(If it were one exercise, I would write the proof in my article, as I have seen in other articles, but in my case there are about five exercises.)



Citing exercises in an article
The answer is essentially given in the comments, so let me summarize:


1. It is a frequent situation that one has to cite an exercise.
2. It is legitimate. (Polya-Szego is cited > 1400 times according to Mathscinet)
3. The best thing is to cite a place where the statement is proved, but if you cannot find such a place, citing an exercise is the second best choice.
4. You can solve the exercise in your paper, or not solve (depending on the difficulty of the exercise and space limitations and other considerations).


And finally my own recommendation: When you refer to an exercise, solve it yourself, no matter whether you include a solution to your paper or not.


Similar considerations apply to handbooks, like Tables of Integrals, etc.
They are essentially made for this purpose, but there are sometimes mistakes,
not frequently. (Gradshtein-Ryzhik is cited > 2200 times according to Mathscinet, Abramowitz-Stegun 1740.)


