But celerity is the speed at which the form moves, the wave form moves. And this is given by obviously, lambda by t and that can also be written as omega by k. Why? Because omega is 2 pi by lambda, K is 2 pi by T. If you can check that lambda by T is nothing but omega by K. You see omega by K is 2pi by lambda divided by 2 pi by T equal to, sorry no. This is K, it will be your omega. See, lambda by T omega, no omega by K is other way round T and this is lambda this is lambda by T. So, we call it celerity as lambda by T omega by k. This is what we can call.