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Mathematical approaches to modeling financial crises have emphasized that there is often positive feedback between market participants' decisions (see strategic complementarity). Positive feedback implies that there may be dramatic changes in asset values in response to small changes in economic fundamentals. For example, some models of currency crises (including that of Paul Krugman) imply that a fixed exchange rate may be stable for a long period of time, but will collapse suddenly in an avalanche of currency sales in response to a sufficient deterioration of government finances or underlying economic conditions.