The Lie Group Structure of the $\eta-\xi$ Space-time and its Physical   Significance
  The $\eta-\xi$ space-time is suggested by Gui for the quantum field theory in 1988. This paper consists of two parts. The first part is devoted to the discussion of the global properties of the $\eta-\xi$ space-time. The result contains a proof which asserts that the $\eta-\xi$ space-time is homeomorphic to $\mathbb{C}^{*}\times \mathbb{C}^{*}\times \mathbb{C}^{2}$ by means of two explicit maps, which shows that the $\eta-\xi$ space-time allows a Lie group structure. Thus some transformation groups, one of which is isomorphic to the Lorentz group in two dimensions, can be found. The other part of the paper is the discussion about the embedding of some subspaces in the $\eta-\xi$ space-time. In particular, it is pointed out that the Euclidean space-time and the Minkowskian space-time are linked in a way in the $\eta-\xi$ space-time such that the tilde field appears naturally. In addition some formulae in the $\eta-\xi$ space-time reappear in a more natural way. 
Zhi-Ming Gu