reserve X for non empty set,
  S for SigmaField of X,
  M for sigma_Measure of S,
  f,g for PartFunc of X,ExtREAL,
  E for Element of S;

theorem Th6:
  Product (<*>ExtREAL) = 1
proof
  Product <*>ExtREAL = multextreal $$ (<*>ExtREAL ) by Def2;
  hence thesis by Th5,FINSOP_1:10;
end;
