I am working with the Nyquist criterion for zero ISI when I find something that makes me think that I misunderstood this criterion.
What Nyquist says is that to avoid ISI in the sampling we must ensure that the sample frecuency is less than 2 times the bandwith of the signal, so if the channel filter is something like a rise cosine the ISI in the sampling will be $0$.
At the same time, we have (another) Nyquist criterion which says that to be able to perfect reconstruct a signal, the sample frequency must be at least $2$ times the bandwith of the signal.
So... taken into account that the case of $F_s=2B$ is not implementable, how can we assure no ISI at the same time that we have perfect reconstruction? Aren't this two criteria contradictory? Am I missing something?