class_docstr: asymmetric negative logistic model of Joe 1990
  
  special case:  a1=a2=1 : symmetric negative logistic of Galambos 1978
  
  restrictions:
   - theta in (0,inf)
   - a1, a2 in (0,1]
code: def _check_args(self, a1, a2, theta):
      condth = theta > 0
      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 AsymNegLogistic obj's underlying member method code with example usage: obj._check_args(a1, a2, theta) and returns: unknown