meta-functioning process allowing Preventing is a type of functioning process of meta-function of "ToPrevent". Two meta-functions "ToAllow" and "ToPrevent" are concerned with the undesirable side effects of functions. A function fa having positive effects on the side effect of a function ft1 is said to have a meta-function “to allow the side-effects of ft1”. The “undesirable side effect” is defined in a relation with another function ft2 or the whole system. The “positive effect” means such a causal relation that increase of the focused attribute of fa causes decrease of the side effect. If a serious trouble (e.g., faults) will be caused in a function ft2 when a function fa is not achieved, function fa is said to have a meta-function “to prevent malfunction of ft2”. For example, the “to super-heat” function of the boiler prevents malfunction of the turbine, because the steam of low temperature would damage the turbine blade by water particles. For almost all fa performing a ToAllow meta-function for ft1, in general, there exists a ToPrevent meta-function for another function ft2.