 So, welcome again and I wish to give you a brief about what you are going to learn in the second week. Now, see in the first week, you learnt several different properties of say system, essentially systems. Properties are associated with systems and you also appreciated that additivity, homogeneity shift invariance were important properties here. These were the properties that you would of course see being obeyed by many non-living systems on a large scale in a large range of operation. Now, what we are going to do in the second week is to establish that you basically the goodness, the good thing about linear shift invariance systems is that you need to perform just one experiment in principle to understand that system completely. So, there you know there is a say something to be gained by modeling a situation as linear and shift invariant. You need to do very little work in principle to understand that system completely. And we are going to identify essentially one input which when given to that system would tell us everything that we want to know about that system. In other words, the complete input-output relationship and that input also is going to be very special. That input if you want me to put it in very plain language is where you just shake the system very briefly and leave it and we are going to call that impulse. So, just excite the system for an infinitesimally small time, but that excitation is strong and then leave it and the response of the system shows if the system is linear and shift invariant will tell us everything that we want to know about the system. Now you can of course watch the videos for the second week and understand what I am saying much better. And in the second week, we are going to embark upon material which is slightly more difficult than what you had in the first week. It will require you to reflect a little bit more in depth. So, please do you know listen to the videos carefully, listen to the lectures carefully, discuss. We would like you to discuss and express what you have not understood because that often is a stumbling block for many learners. This whole idea of impulse response, step response, a relation between them, this requires some thinking and some reflection to understand. But it is a very important part of the whole course on signal and system. So, please take the trouble to appreciate this material properly. Well, see you in the next week and good luck. We look forward to active discussion again. Thank you.