  Let $n, m, k$ be positive integers with $k=n-m+1$. We establish an abstract
Morse-Sard-type theorem which allows us to deduce, on the one hand, a previous
result of De Pascale's for Sobolev $W^{k,p}_{\textrm{loc}}(\mathbb{R}^n,
\mathbb{R}^m)$ functions with $p>n$ and, on the other hand, also the following
new result: if $f\in C^{k-1}(\mathbb{R}^n, \mathbb{R}^m)$ satisfies
$$\limsup_{h\to 0}\frac{|D^{k-1}f(x+h)-D^{k-1}f(x)|}{|h|}<\infty$$ for every
$x\in\mathbb{R}^n$ (that is, $D^{k-1}f$ is a Stepanov function), then the set
of critical values of $f$ is Lebesgue-null in $\mathbb{R}^m$. In the case that
$m=1$ we also show that this limiting condition holding for every
$x\in\mathbb{R}^n\setminus\mathcal{N}$, where $\mathcal{N}$ is a set of zero
$(n-2+\alpha)$-dimensional Hausdorff measure for some $0<\alpha<1$, is
sufficient to guarantee the same conclusion.
