Until Wednesday, no country had ever sold 10-year debt that gives investors a yield of below 0%. And no country had ever issued a 100-year bond denominated in euros.

But in the latest stark sign of how easy the era of easy money has become, Switzerland on Wednesday sold 10-year bonds that investors are actually paying to hold, while Mexico lined up a rare transaction to borrow euros it promised to repay a century from now—at a yield of 4.2%.

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