The real economic cycle is the phenomenon of periodic economic expansion and contraction in the process of production and reproduction in market economy. In economic analysis, each cycle is generally divided into four stages, namely, prosperity stage, depression stage, crisis stage and recovery stage. Or it can be divided into two stages and two turning points, that is, the crisis stage is regarded as the turning point from prosperity to decline, and the recovery is regarded as the turning point from decline to prosperity. In the book Business Cycle: Problems and Settings published by 1927, Mitchell believes that a complete economic cycle should go through four stages: prosperity, recession, depression and recovery. Dividing an economic cycle into four stages or two turning points is a common feature summed up from historical experience. /kloc-since the middle of the 0/9th century, people have studied the cycle phenomenon that plagues economic operation and put forward different lengths and types of cycles. ?

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