Let $X$ be a Polish space. Assume that $(C_m)_{m\in\mathbb{N}}$ is an increasing sequence of compact subsets of $X$ and denote $C=\bigcup_{m}C_m$. Let $\{f_n:n\in\mathbb{N}\}$ be a family of functions from $X$ in $\left[0,1\right]$, which is equicontinuous on compact subsets of $X$.
By the Arzelà-Ascoli theorem we can find a subsequence $(f_{k_n})_{n\in\mathbb{N}}$ convergent to a function $f$ uniformly on the set $C_m$, for any $m \in \mathbb{N}$.
Naturally $f$ is continuous on each set $C_m$, but a function with this property need not to be continuous on the set $C$.
Can one choose a subsequence in such a way that the limit be a continuous function on $C$?
As for me, this concept is too optimistic, but it was used in the paper Remarks on Ergodic Conditions for Markov Processes on Polish Spaces by Stettner (page 110, step 3).