I've been asked how I know information flows from the demand to the supply several times, most recently by commenter Jamie and David Glasner. The easiest answer is that I don't really know, but just assumed that for now. However there are some plausible arguments that I will try to clearly present here. For concreteness, let's call I(D) the information sent (or received) by "the demand" and I(S) the information received (or sent) by "the supply".