Hi. I want to know what you think about this, that's why I write this message. According to the function u(t): ____ | 1, t>0 u(t)=| ?, t=0 ____ | 0, t<0 What do U think about the value of the function u(t) when time is 0? Is it define? or not? Some books say that the value is 1, but others don't. According to general knowledge in books, what do they say? What do you think? Bye. Ingyil.