Method register4

ar.py:371–374

(
      self, a: str, b: str, c: str, d: str, dep: pr.Dependency
  )

    self.register([(a, 1), (b, -1), (self.const, -f)], dep)

  def register4(
      self, a: str, b: str, c: str, d: str, dep: pr.Dependency
  ) -> None:
    self.register([(a, 1), (b, -1), (c, -1), (d, 1)], dep)

  def why(self, e: dict[str, float]) -> list[Any]:
    """AR traceback == MILP."""