code: def fermionic_constraints(a):
      
      substitutions = {}
      for i, ai in enumerate(a):
          substitutions[ai ** 2] = 0
          substitutions[Dagger(ai) ** 2] = 0
          substitutions[ai * Dagger(ai)] = 1.0 - Dagger(ai) * ai
          for aj in a[i+1:]:
              # substitutions[ai*Dagger(aj)] = -Dagger(ai)*aj
              substitutions[ai*Dagger(aj)] = -Dagger(aj)*ai
              substitutions[Dagger(ai)*aj] = -aj*Dagger(ai)
              substitutions[ai*aj] = -aj*ai
              substitutions[Dagger(ai) * Dagger(aj)] = - Dagger(aj) * Dagger(ai)
  
      return substitutions
docs: Return  a set of constraints that define fermionic ladder operators.
  
      :param a: The non-Hermitian variables.
      :type a: list of :class:`sympy.physics.quantum.operator.Operator`.
      :returns: a dict of substitutions.