FWIW, I agree with wnoise, public funding of a library is a subsidy for the users of the library. If publicly funded libraries didn't exist, privately funded ones would, and those privately funded libraries would charge people money just as surely as a privately funded museum charges admissions. (And they'd probably have a "Second Tuesday of the month is free" special, much like a museum.)

Note: when I say something is a "subsidy" I am attempting to state a fact, not attempting to make a moral judgment. In the specific case of a public library, I think they're overdone and a bit of an applause light but ultimately a good use of community tax dollars. But if something costs tax dollars, and it does not benefit the people taxed in proportion to the amount of tax taken from them, then this is the thing that I am referring to when I use the label "subsidy". (The matter is, of course, complicated because "benefit" is much more nebulous than "direct benefit".)