Quasi Extended Chebyshev spaces and weight functions

We recently showed that the class of Quasi Extended Chebyshev spaces is the largest class of sufficiently differentiable functions permitting design. In previous articles we mentioned a simple procedure to build such spaces by means of both generalised derivatives associated with non-vanishing weight functions and two-dimensional Chebyshev spaces. In the present one we prove that, conversely, on a closed bounded interval, any Quasi Extended Chebyshev space can be obtained via the latter procedure. We then draw a few interesting consequences from the latter result.