Eugene Roche, UCD Library Special Collections & Stewart McKee, UCD Library Collections.
Enclosures in books (this would include almost anything that is extraneous to the text and was inserted after publication: it could include bookmarks, correspondence, shopping lists, bus tickets or notes referring to the text or other matters) can be prove to be in some instances much more valuable that the book that actually contains them.
Below is one unearthed by UCD Library colleague Stewart McKee while weeding in the library Store. The value of the letter lies essentially in the signature but the book gains value also as it gives the context in which the letter was written i.e. Taoiseach De Valera writing to Michael Hogan, Professor of Civil Engineering at UCD, in 1958 to thank him for his work on the Atomic Energy Report (a report which, incidentally, called for the construction of a trial nuclear reactor at an unspecified “Dublin university”). Book and report will reside permanently in UCD Special Collections.