two characters a and B but rather things like distributions over images represented by latent variable models so there's this very nice algorithm introduced in 2019 called bits back with ans or BB ans which is its back coding using ans as a back end and the the reason to use ans is because it turns out that the the staff like property of ans where the last thing you decode or the wear whatever you decode is the last in Unicode makes it very compatible with the concept of getting bits back so let's just see how that works so here