Thanks Arthur. I've deleted your post to keep the thread "clean"
Solitude starts without a library, you will have to cooperate during those first seasons.
You can trade books with magi from other covenants at tribunal a character attends or if a character uses a season for it.
Book trades are based on build point value - so you give away (copies of) books worth 40 bp and get books worth 40 bp. You can only trade art books for art books and ability books for ability books.
I will do the book-keeping in this thread. Please do not post in it.
If you trade away summae, you can only acquire summae in return whose level is limited to the highest summa you trade away.
Only at a tribunal, you can trade away up to three copies of the same book (if fewer copies are traded away, the other copies cannot be sold later). Otherwise a copy of a book can only be traded away once. Books acquired by trade cannot be traded away at all.
Corebook-spells invented at Solitude can be traded for other corebook spells 1:1.
Other labtexts (non-corebook spells, enchantments) made at Solitude are less interesting for other magi, lowering the ratio to 2:1.
The number of copies that can be sold is handled the same way as for books.
Vis can be traded at Tribunal the following rates
2p form : 1p technique
1p form : 1 p form
On other occasions, a magus can get those rates if he spends a season on trading, or can use the Redcaps (rules from HoH:TL)
There are more complex trades, of course, like a gently gifted apprentice and a longevity ritual for two magical cats useable as familiars plus a few tractatus. I'll handle those situations when they arise.
You don't have to roll dice, but:
Success on a communication+bargaining roll can get you a better deal, a poor result means you get less. Only magi can make those deals.
All of this is not the most realistic way of dealing with things, but keeps book-keeping doable.