HOW_GOOD is a function with input [A, an action [and a hypothesis]] and output [0;1].
Score(action) is another extended sum. For every h in HYPOTHESIS, we calculate PRIOR(h) * LOOKS_LIKE_THIS_WORLD(h) * HOW_GOOD(action, h). Sum them up, and we get Score(action).
rotatingpaguro comments on [missing post]