Time Invariant System
If the cascade x(t)--->[time delay by t0]--->[system]---->z(t)
yields the same output as the cascade
x(t)--->[system]--->[time delay by t0]--->y(t) for any t0, then the
system is called "time invariant".
Time variant System
If the cascade x(t)--->[time delay by t0]--->[system]---->z(t)
does not yield the same output as the cascade
x(t)--->[system]--->[time delay by t0]--->y(t) for any t0, then the
system is called "time variant".
