Explosions inside Ejecta and Most Luminous Supernovae
  The extremely luminous supernova SN2006gy is explained in the same way as other SNIIn events: light is produced by a radiative shock propagating in a dense circumstellar envelope formed by a previous weak explosion. The problems in the theory and observations of multiple-explosion SNe IIn are briefly reviewed. 
S.I.Blinnikov (ITEP, Moscow and RESCEU, Tokyo; currently at IPMU,   Tokyo)