In this regard, it is crucial to understand the role of walls and other "constraints", and the distinction between "independent" processes and "coupling". Contrary to the clear implications of many reference sources, the previous analysis is not restricted to , isotropic bulk systems which can deliver only "P"d"V" work to the outside world, but applies even to the most structured systems. There are complex systems with many chemical "reactions" going on at the same time, some of which are really only parts of the same, overall process. An "independent" process is one that "could" proceed even if all others were unaccountably stopped in their tracks. Understanding this is perhaps a “thought experiment” in chemical kinetics, but actual examples exist.