De Guilleuma investigated a reference in a book published in 1609 by the Italian Girolamo Sirtori.

BBC: Controversy over telescope origin

These "known unknowns" he dubbed "grey swans", in a reference to Nicholas Nassim Taleb's book "The Black Swan", about the nature of unpredictability.

BBC: WPP Martin Sorrell says tax 'a question of judgement'

But it is an excellent reference book for anyone wanting a better understanding of economic developments in the last millennium.

ECONOMIST: World trade

L. James's book, you will know that the Grey in question is one of the protagonists rather than a reference to a fashion lexicon.

WSJ: Tina Gaudoin on Style: Twenty Five Shades of You Know What��

Bizarrely, one of Dr Lomborg's critics in Scientific American criticises as an affectation the book's insistence on documenting every statistic and every quotation with a reference to a published source.

ECONOMIST: ��The Skeptical Environmentalist��