**W**hile waiting for Jean-Michel to leave a thesis defence committee he was part of, I read this recently arXived survey by Novak and Rudolf, Computation of expectations by Markov chain Monte Carlo methods. The first part hinted at a sort of Bernoulli factory problem: when computing the expectation of * f *against the uniform distribution on

**,**

*G*

Forx ∈ Gwe can computef (x)andGis given by a membership oracle, i.e. we are able to check whether anyxis inGor not.

However, the remainder of the paper does not get (in) that direction but recalls instead convergence results for MCMC schemes under various norms. Like spectral gap and Cheeger’s inequalities. So useful for a quick reminder, e.g. to my Monte Carlo Statistical Methods class Master students, but altogether well-known. The paper contains some precise bounds on the mean square error of the Monte Carlo approximation to the integral. For instance, for the hit-and-run algorithm, the uniform bound (for functions *f* bounded by 1) is

where * d* is the dimension of the space and

*a scale of the volume of*

**r***. For the Metropolis-Hastings algorithm, with (independent) uniform proposal on*

**G***, the bound becomes*

**G**where * C* is an upper bound on the target density (no longer the uniform). [I rephrased Theorem 2 by replacing vol(G) with the containing hyper-ball to connect both results, α

_{d}being the proportionality constant.] The paper also covers the case of the random walk Metropolis-Hastings algorithm, with the deceptively simple bound

but this is in the special case when G is the ball of radius d. The paper concludes with a list of open problems.