On Geometric Properties of Triangularizations for Nonlinear Control Systems

Necessary and Sufficient Conditions for the Linearizability of Two-Input Systems by a Two-Dimensional Endogenous Dynamic Feedback

“…However, the second systems in (11) is a negative example, it does not meet the conditions for flatness with d ≤ 2 2 , so we can conclude that if the system is flat, it must have a difference of d ≥ 3. (The system is indeed flat with a difference of d = 3, in e. g. Schöberl and Schlacher (2015) a corresponding flat output with d = 3 has been derived. )…”