  J. Marcinkiewicz and A. Zygmund proved in 1936 that the special $n$-th
generalized Riemann derivative $\widetilde{D}_nf(x)$ with nodes
$0,1,2,2^2,\ldots, 2^{n-1}$, is equivalent to the $n$-th Peano derivative
$f_{(n)}(x)$, for all $n-1$ times Peano differentiable functions $f$ at~$x$.
Call every $n$-th generalized Riemann derivative with this property an MZ
derivative. A recent paper by the authors introduced the $n$-th Gaussian
derivatives as the $n$-th generalized Riemann derivatives with nodes either
$0,1,q,q^2,\ldots ,q^{n-1}$ or $1,q,q^2,\ldots ,q^{n}$, where $q\neq 0,\pm 1$,
proved that the Gaussian derivatives are MZ derivatives, and conjectured that
these are all MZ derivatives. In this article, we invalidate the conjecture in
three different ways, by scales of generalized Riemann derivatives, by
reference to the classification of generalized Riemann derivatives, and by
means of an independent counterexample. In addition, we show that Riemann
differentiation is not equivalent to a Gaussian differentiation in orders at
least three, find an explicit description of the equivalence class of a
generalized Riemann derivative, and prove a more general quantum analogue of
the GGR Theorem. The symmetric versions of all these results are also included
in the article.
