content_image/388760.jpg content_image/388763.jpg content_image/388770.jpg content_image/388764.jpg content_image/388769.jpg
<img src='content_image/388760.jpg'>

<img src='content_image/388763.jpg'>

respectively. 

Comparison of the diagrams of Fig.1 for the G ( n ) αα ′ ( n -th order of perturbation theory for the one-particle propagator) to the contributions of Fig.2 for 〈 U n +1 λ ( β ) 〉 c 0 (( n + 1)-th order for evolution operator) allows us to es- tablish the following simple relation ( n ≥ 1): 

<img src='content_image/388770.jpg'>

and as the result we have 

<img src='content_image/388764.jpg'>

Taking into account equations (12) and (13) we obtain 

<img src='content_image/388769.jpg'>

