essentially we're just redefining the rectangle as being only only let's say this part that's our new rectangle and that's the only part of the world we're working with possible States you can take on and once we've done that we put all probability on this thing we kind of renormalize it everything's there that's our new rectangle and the maths not going to change because we're just looking at this sub part of the whole rectangle but of course you need to do it consistently every step along the way we need to consistently look at that sub