Probability help neededWatch
Could do with a hint on this please: it seems fairly obvious but not sure how to go about a proof.
Also, you can look at the 1 on the right-hand-side of the result we want. Where must it come from? It must come from our mapping P being a probability measure, and so P(the whole space) = P(R) = 1. Can we write R in terms of our sets defined above?