code: def add(self, rule: ControlRule = None, *, supply: float):
          
          if supply in self._thresholds:
              raise ValueError('rule for threshold %s re-defined' % supply)
          if rule is not None:
              self.rules.append((supply, rule))
              self._thresholds.add(supply)
              return rule
          else:
              return partial(self.add, supply=supply)
docs: Register a new rule above a given ``supply`` threshold
  
          Registration supports a single-argument form for use as a decorator,
          as well as a two-argument form for direct application.
          Use the former for ``def`` or ``class`` definitions,
          and the later for ``lambda`` functions and existing callables.
  
          .. code:: python
  
              @control.add(supply=10)
              def linear(pool, interval):
                  if pool.utilisation < 0.75:
                      return pool.supply - interval
                  elif pool.allocation > 0.95:
                      return pool.supply + interval
  
              control.add(
                  lambda pool, interval: pool.supply * (1.2 if pool.allocation > 0.75 else 0.9),
                  supply=100
              )