code: def deriv2_inverse(self, phi, theta):
      et = np.exp(theta)
      ept = np.exp(phi + theta)
      d2 = (et - 1) * ept / (theta * (ept - et + 1) ** 2)
      return d2
  
imports: import warnings
  import numpy
  from scipy.special import expm1, gamma
label_desc: Use image node_id 5 for calling the TransfFrank obj's underlying member method code with example usage: obj.deriv2_inverse(phi, theta) and returns: d2