Leading logarithmic contribution to the second-order Lamb shift induced   by the loop-after-loop diagram
  Contribution of order \alpha^2 (Z \alpha)^6 \ln^3(Z \alpha)^{-2} to the ground-state Lamb shift in hydrogen induced by the loop-after-loop diagram is evaluated analytically. An additional contribution of this order is found compared to the previous calculation by Karshenboim [JETP 76, 541 (1993)]. As a result, an agreement is achieved for this correction between different numerical and analytical methods. 
Vladimir A. Yerokhin