Basic signal analysis (system invertible)

[FrogPad]

Ok I have this really simple question that is bugging me.

Lets say you have the signal:

y(t) = x(t-4)

where y(t) corresponds to the output, and x(t) the input.

I know this system is invertible, but I don't really know how to show that this is the case. I see that the output is x(t) with an independet variable transformation such that the input shifted by 4 units to the right. So if we shift the output four units to the left then we get the input without the independent variable transformation. I just don't know how to express what is going on here mathematically.


Maybe I don't understand invertibility well enough to apply it.
From what I gather it can be shown by,

x(t) --> [system] --> y(t) = T{x(t)}
y(t) --> [invert] --> T{y(t)} = x(t)

I'm getting confused since the problem has x(t-4) in this case. I'm guessing I can show it with some type of function composition, but I need some help.

thanks

 

[marcusl]

You can make the substitution
t' = t - 4
so that
x(t') = y(t'+4)
The inverted function is non-causal, since you need to know future values of y to find the present value of x.