Time Invariance
A system is Time Invariant if and only if the response to the shifted input is equal to the shifted output.
x(t-t0) -System-> y(t-t0)
x(t) -System-> z(t) -Time Shift t0-> z(t-t0) == y(t-t0)
A system is Time Variant if the shifted input is not equal to the shifted output.
x(t-t0) -System-> y(t)
x(t) -System-> z(t) -Time Shift t0-> z(t-t0)
