If $\{D_{n}\}_{{n\in\mathbb{N}}}$ and $\{E_{n}\}_{{n\in\mathbb{N}}}$ are distribution ensembles (on $\Omega$) then we say they are computationally indistinguishable if for any probabilistic, polynomial time algorithm $A$ and any polynomal function $f$ there is some $m$ such that for all $n>m$:

where $\operatorname{Prob}_{A}(D_{n})$ is the probability that $A$ accepts $x$ where $x$ is chosen according to the distribution $D_{n}$.