Equivalence of Different Realization Methods for Higher Order Nonlinear Input ­ Output Differential Equations

When different approaches to a certain subject are ripe enough, this is usually a good moment for an attempt to compare them and to unify different paths into one well-paved way. However this usually requires a hard work and is often a nonprofit activity. The hard thing is finding a common language and good notation, in which all these different approaches could be nicely expressed. And often it appears that what one gets looks like a simple exercise or is a part of the unwritten folk knowledge. Nevertheless someone has to do such a job, as this is a necessary step in building up a foundation of a higher level theory. Kotta and Mullari have undertaken a job of comparing different realization methods for higher order nonlinear input–output differential equations. By realization of the equation