This note presents an exposition which unifies various (static or dyna
mic feedback) solutions given in the literature to the disturbance dec
oupling problem since the early development of modern nonlinear theory
up to the end of the 70's. This is possible thanks to some recently i
ntroduced generalized transformations depending on a finite number of
time derivatives of the input. In this way, some classical controlled
invariant distributions can be replaced by a related elementary linear
subspace by which a NSC for disturbance decoupling can be derived.