Questions tagged [causality]

I guess the same question is usually asked for complex numbers too, but the fact is that complex numbers are used all the time practically. However, at least on a quick google search, I couldn't find any applications of anticausal systems. So why…

The book states: Causality implies that, if x1[n] = x2[n] for n <= n0, then y1[n] = y2[n] for n <= n0. But isn't it always the case, that for same inputs we're getting same outputs except for the case of time-variance, which this sentence is not…