So we know that just like proteins are synthesized and eventually placed into the membrane in an asymmetric fashion, lipids are also synthesized and inserting to the membrane asymmetrically. However, the thing about lipids is, so fossil lipids is they can actually flip flop, they can actually rotate. And so what that implies is, unlike the absolute configuration, unlike the absolute asymmetry of the proteins in the membrane that basically do not change because they cannot flip flop, the asymmetry of the membrane due to the lipids does in fact change over time. It is not absolute because these lipids can actually rotate, can actually flip flop from one leaflet to the other. So we see that however, lipids such as fossil lipids can actually flip flop and therefore the asymmetry of the fossil lipids in that membrane does not remain absolute, it changes over time. However, we know that flip flopping of fossil lipids actually takes place very, very slowly because it is also energetically unfavorable.