inverse so we have an approximate inverse and they basically suggest if we have an approximate inverse we can do the phone so G G is now an approximate inverse to F what we can do is this is our input signal right we use F to map it forward to this and so on all the way up until we get our true or error right here this is our error from the environment right this is the nail being wrong and then we do two applications of G right so this is an application of F we do to applet of g1 we applied g2 this to what we got