## A chance non-typo

A few days ago, my colleague Medhi Dafal in the admin branch of the university came across Monte Carlo Statistical Methods on another colleague’s desk and took it with him. Yesterday morning, when I came to his office to burden him with another admin nightmare, he opened the book [at random] and pointed out a formula pretending he had trouble with it! This was the residual distribution in the Markov chapter

$\tilde K(x,\cdot)=\dfrac{K(x,\cdot) - \epsilon\mathbb{I}_C(x)\nu(\cdot)}{1-\epsilon\mathbb{I}_C(x)}$

When I first saw it, I though this was indeed a typo because of the indicator in the denominator. Now that I look at it more carefully, I realise this is correct, because C is a small set, hence the residual kernel is the standard kernel outside C. Still, for a few minutes, I had this weird impression he had found a new typo completely at random! Which would have been a significant item of information about the frequency of typos in this book… Phew!

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