code: def trim(self, lower=None, upper=None):
          
          if upper is None:
              upper = self.subseqs.seqs.model.parameters.control.nfk
          lland_sequences.State1DSequence.trim(self, lower, upper)
docs: Trim values in accordance with :math:`BoWa \\leq NFk`.
  
          >>> from hydpy.models.lland import *
          >>> parameterstep('1d')
          >>> nhru(5)
          >>> nfk(200.)
          >>> states.bowa(-100.,0., 100., 200., 300.)
          >>> states.bowa
          bowa(0.0, 0.0, 100.0, 200.0, 200.0)