For instance, whereas a government can easily freeze or even seize a bank account located in its jurisdiction, it’s very difficult for it to do the same with funds held in cryptocurrency — even if the holder is a citizen or legal resident.
Although this test successfully detects single isolated bubbles, Phillips, Shi, and Yu [24] acknowledge it may suffer from reduced discriminatory power when applied to time series with multiple occurrences of bubbles. To overcome this weakness, a further enhancement was proposed, as a new method, called a generalized supremum ADF (GSADF) test. This test allows both the start and end points of data subsets to vary, which in turn enables the identification of multiple bubble regimes in one observed time series. The GSADF test is defined by

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Once they have a key, they can obtain and spend cryptocurrency. Without the key, the holder can’t spend or convert their cryptocurrency — rendering their holdings worthless unless and until the key is recovered.