code: def mom_111(self, idxi, idxj, idxk):
          
          if (idxi, idxj, idxk) in self.hist:
              return self.hist[idxi, idxj, idxk]
  
          if idxi == idxk == 0 or idxi == idxj == 0:
              out = 0
  
          elif chaospy.bertran.add(idxi, idxk, self.dim) < idxj \
                  or chaospy.bertran.add(idxi, idxj, self.dim) < idxk:
              out = 0
  
          elif chaospy.bertran.add(idxi, idxj, self.dim) == idxk:
              out = 1
  
          elif idxj == idxk == 0:
              out = self.dist.mom(chaospy.bertran.multi_index(idxi, self.dim))
  
          elif idxk == 0:
              out = self.mom_110(idxi, idxj, idxk)
  
          else:
              out = self.mom_recurse(idxi, idxj, idxk)
  
          self.hist[idxi, idxj, idxk] = out
  
          return out
docs: Backend moment for i, j, k == 1, 1, 1.