Abe Books
Just thought I'd mention this excellent source of second-hand books https://www.abebooks.co.uk - I'm particularly pleased with it this morning as it turns out that one of the books I ordered is coming from an educational charity - so much better than Amazon (though the reason I'm buying second-hand is because two seem to be only available new from Australia, with a seven-month wait - I do prefer a pristine copy, I admit, though it's not a very ecological approach).
