def ForneyFactorGraph(FactorGraph):
    """Class  for Forney-style factor graphs.

    A Forney-style factor graph represents the factorization of a function of
    several variables. Assume, for example, that some function
    f(x1, x2, x3, x4) can be factored as

        f(x1, x2, x3, x4) = fa(x1, x2) fb(x2, x3) fc(x2, x4).

    The factor graph representing the factorization is given as

      x1  +----+  x2 +----+ x2' +----+  x3
     -----| fa |-----| =  |-----| fb |-----
          +----+     +----+     +----+
                       |
                       | x2''
                       |
                     +----+
                     | fc |
                     +----+
                       |
                       | x4.
                       |

    The class for Forney-style factor graphs is inherited from the base class
    for factor graphs.

    """

    def __init__(self):
        """Initialize a Forney-style factor graph."""
        super().__init__(self)
