As any, even vaguely addicted book collector will have swiftly learned, most booksellers' catalogues are written in a parallel language that can fool anyone but the cognoscenti and which makes the mysteries of the Rosetta Stone look like something out of Enid Blyton. Without a smattering of inside information, the baffled but hopelessly-bitten book buyer is drifting unarmed and unprepared into a minefield whose perilous complexities will usually only be made plain when an eagerly awaited parcel