If I hadn't been here, you would have had to ask yourself these questions and answer them by thinking, looking in a reference book, or consulting a friend.

如果我不在这儿，你可以向自己提问，然后通过思考，查阅参考书或请教朋友去弄懂它们。

youdao

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

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

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

ECONOMIST: World trade