Fuzzy sets over evolving universes

Fuzzy membership functions may be defined over universes of discourse that are not fixed and well known but that instead are subject to evolution, that is to say universes of discourse that change over time according to some probability distribution. In such a case, the value of the membership functions will depend upon the probability distribution defined on the universe. If the distribution is unknown, then a procedural way of producing good approximations of the membership function is needed.