  This paper proposes a new mathematical framework that can be applied to
biological problems such as analysis of the structures of proteins and protein
complexes. In particular, it gives a new method for encoding the
three-dimensional structure of a protein into a binary sequence, where proteins
are approximated by a folded tetrahedron sequence. It also gives a new
algebraic framework for describing molecular complexes and their interactions.
  For simplicity, we shall explain the framework in the case of two-dimensional
objects. Then, the binary code of a plane curve is obtained as the ``second
derivative'' of the curve and ``fusion and fission'' of closed trajectories is
described algebraically.
