(1) Definitions, properties.
      - torsion of an acyclic complex
      - torsion of a CW-complex
      - properties
      - classification of lens spaces
(2) Alexander polynomial and twisted Alexander polynomial.
      - Milnor's theorem: Alexander polynomial=Reidemeister torsion.
      - twisted Alexander polynomials=Reidemeister torsion.
(3) Application of twisted Alexander polynomial
      - Criterion for the non-existence of an epimorphism
(4) Reidemesiter torsion of a homology 3-sphere
      - Dennis Johnson's theory and its generalization
(5)Ray-Singer torsion, L2-torsion and hyperbolic volume