code: def _one_body_mapping(a_i, a_j, threshold=0.000001):
          
          pauli_list = []
          for alpha in range(2):
              for beta in range(2):
                  pauli_prod = Pauli.sgn_prod(a_i[alpha], a_j[beta])
                  coeff = 1.0/4 * pauli_prod[1] * np.power(-1j, alpha) * np.power(1j, beta)
                  pauli_term = [coeff, pauli_prod[0]]
                  if np.absolute(pauli_term[0]) > threshold:
                      pauli_list.append(pauli_term)
          return Operator(paulis=pauli_list)
docs: Subroutine for one body mapping.
          Args:
              a_i (Pauli): pauli at index i
              a_j (Pauli): pauli at index j
              threshold: (float): threshold to remove a pauli
          Returns:
              Operator: Operator for those paulis