These shifts are defined via parametric changes in the causal mechanisms of observed variables, where constraints on parameters yield a "robustness set" of plausible distributions and acorresponding worst-case loss overthe set.
Thisisespecially apparent in natural language, which is often described as a tool for making'infinite use of finite means' [8]. Previously acquired words canbeinfinitely nested using asetofgrammatical rules to communicate an arbitrary thought, opinion, or state one is in.