code: def destruct(particles, index):
      
  
      mat = np.zeros((2**particles, 2**particles))
  
      flipper = 2**index
      for i in range(2**particles):
          ispin = btest(i, index)
          if ispin == 1:
              mat[i ^ flipper, i] = phase(i, index)
      return csr_matrix(mat)
docs: Fermion annihilation operator in matrix representation for a indexed
         particle in a bounded N-particles fermion fock space