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A class of models for relaxation in strongly interacting glassy materials is suggested. Degrees of freedom are divided into a sequence of levels such that those in level n+1 are locked except when some of those in level n find the right combination to release them, this representing the hierarchy of constraints in real systems. The Kohlrausch anomalous relaxation law, exp- (t{) }^, emerges naturally, and a maximum time scale is found which exhibits a Vogel-Fulcher-type temperature dependence.
Palmer et al. (Mon,) studied this question.