docs: def _scalar_coef_op_left(func):
          """decorator for operator overloading when ScalarCoef is on the
          left"""
          @wraps(func)
          def verif(self, scoef):
              if isinstance(scoef, ScalarCoefs):
                  if len(self._vec) == len(scoef._vec):
                      return ScalarCoefs(func(self, self._vec, scoef._vec),
                                          self.nmax,
                                          self.mmax)
                  else:
                      raise ValueError(err_msg['SC_sz_msmtch'] % \
                                      (self.nmax, self.mmax,
                                       scoef.nmax, scoef.mmax))
          
              elif isinstance(scoef, numbers.Number):
                  return ScalarCoefs(func(self, self._vec, scoef), self.nmax,
                                     self.mmax)
              else:
                  raise TypeError(err_msg['no_combi_SC'])
          return verif