A Blackwell $\epsilon$-optimal strategy in a Markov Decision Process is a strategy that is $\epsilon$-optimal for every discount factor sufficiently close to 1.
We prove the existence of Blackwell $\epsilon$-optimal strategies in finite Markov Decision Processes with partial observation.
"Blackwell optimality in Markov decision processes with partial observation." Ann. Statist. 30 (4) 1178 - 1193, August 2002. https://doi.org/10.1214/aos/1031689022