  We would like to congratulate the authors of "A Bayesian Conjugate Gradient
Method" on their insightful paper, and welcome this publication which we firmly
believe will become a fundamental contribution to the growing field of
probabilistic numerical methods and in particular the sub-field of Bayesian
numerical methods. In this short piece, which will be published as a comment
alongside the main paper, we first initiate a discussion on the choice of
priors for solving linear systems, then propose an extension of the Bayesian
conjugate gradient (BayesCG) algorithm for solving several related linear
systems simultaneously.
