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Folds that form passively by taking a form that may match best with that of the most competent layer in a complex as is found in the zone of contact strain such as 1A to 1B in outer and 3 in inner arc regions. These folds are typical 1C folds of Ramsay with t' less than unity as the mean geometry of the complex pulsating between 1B and 3 (ignoring 2). For this reason, similar or class 2 folds are also called passive in which the layers do not take an active part in buckling.