code: def less_than_obs_constraints(self):
          
  
  
          obs = self.observation_data
          lt_obs = obs.loc[obs.apply(lambda x: self._is_less_const(x.obgnme) \
                                               and x.weight != 0.0,axis=1),"obsnme"]
          return lt_obs
docs: get the names of the observations that
          are listed as less than inequality constraints.  Zero-
          weighted obs are skipped
  
          Returns
          -------
          pandas.Series : obsnme of obseravtions that are non-zero weighted
                          less than constraints