class_docstr: asymmetric logistic model of Tawn 1988
  
  special case: a1=a2=1 : Gumbel
  
  restrictions:
   - theta in (0,1]
   - a1, a2 in [0,1]
code: def _check_args(self, a1, a2, theta):
      condth = (theta > 0) and (theta <= 1)
      conda1 = (a1 >= 0) and (a1 <= 1)
      conda2 = (a2 >= 0) and (a2 <= 1)
      return condth and conda1 and conda2
  
imports: import numpy
  from scipy import stats
  from statsmodels.tools.numdiff import _approx_fprime_cs_scalar, approx_hess
label_desc: Use image node_id 1 for calling the AsymLogistic obj's underlying member method code with example usage: obj._check_args(a1, a2, theta) and returns: unknown