“2024阿里巴巴全球数学竞赛”初赛7道题，只有第1道组合题较简单，用高中数学可解，其他都是很难的高等数学，2、6用到概率论；3、4是高级线性代数，数学系课程；5是拓扑学，也是数学系课程；7用到微分方程。所以必须系统学过数学系本科课程才能考好，那些进入决赛的十几个初中生、二十几个高中生也大部分（如果不是全部的话）都是别人代考。不排除个别数学天才在中学已系统学过数学系课程，但这么多那真是神州大地天才辈出了，有的还是初一、初二学生呢。阿里巴巴搞这种可以作弊的开卷竞赛有什么意义？难道不知道中国是作弊大国？

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Date: 2024-06-19| 方舟子

Should I buy bitcoin?

“To the extent it is used I fear it’s often for illicit finance. It’s an extremely inefficient way of conducting transactions, and the amount of energy that’s consumed in processing those transactions is staggering,” the former Fed chairwoman said. Yellen’s comments have been cited as a reason for bitcoin’s recent losses. However, Yellen’s assessment of bitcoin as a inefficient medium of exchange is an important point and one that has already been raised in the past by bitcoin bulls. Using a volatile asset in exchange for goods and services makes little sense if the asset can tumble 10% in a day, or surge 80% over the course of a two months as bitcoin has done in 2021, critics argue. To put a finer point on it, over the past 12 months bitcoin has registered 8 corrections, defined as a decline from a recent peak of at least 10% but not more than 20%, and two bear markets, which are defined as falls of 20% or more, according to Dow Jones Market Data.

The S&P 500 slumped 1.8% on Monday and Tuesday, thanks to China Evergrande, the Chinese property company that looks like it is ready to default on its more-than $300 billion in debt. Cries of the next Lehman Brothers—or maybe the next Silverado?—echoed through the canyons of Wall Street as investors prepared for the worst.