Consider the set of continuous maps $C^0([0,1],[0,1])$ equipped with the compact-open topology. It is metrisable, and therefore sequential. It is also a k-space: see <http://neil-strickland.staff.shef.ac.uk/courses/homotopy/cgwh.pdf> Proposition 1.6. The proof relies on the facts that every k-closed subset is in particular $\overline{\mathbb{N}}$-closed where $\overline{\mathbb{N}}$ is the one-point compactification of $\mathbb{N}$, that every $\overline{\mathbb{N}}$-closed subset is sequentially closed, and therefore the kelleyfication functor adds no open subsets in the topology. Since $\overline{\mathbb{N}}$ is not $\Delta$-generated (its $\Delta$-kelleyfication is the discrete space $\overline{\mathbb{N}}^\delta$), the preceding proof does not work for $\Delta$-generated spaces.



> 
> I am (almost) sure that $C^0([0,1],[0,1])$ is not $\Delta$-generated
> and I would appreciate to see a proof.
> 
> 
> 


**Motivation**: This question is important for me because I am trying to understand specific things about the topology of the space of execution paths of a cellular multipointed $d$-space having a finite number of cells (in the sense of <https://arxiv.org/abs/1904.04159>). And the space above appears everywhere.



Compact-open topology and Delta-generated spaces
The mapping space $C([0,1],[0,1])$ in the compact-open topology is in fact $\Delta$-generated.


The reason for this is that every locally path-connected first-countable space is $\Delta$-generated. This was proved by Christensen, Sinnamon, and Wu in Proposition 3.11 of their paper [*The D-Topology for Diffeological Spaces*](https://msp.org/pjm/2014/272-1/), Pacific J. Math., **272**, (2014). As has already been noted, $C([0,1],[0,1])$ is metrisable, and hence first-countable. In addition it's not difficult to see that it is also locally path-connected (in fact it is locally contractible in a strong sense).


