class_docstr: A wild token that matches conditionally.
  
  arg   - a wild token.
  valid - an additional constraining function on a match.
code: def __init__(self, arg, valid):
      self.arg = arg
      self.valid = valid
  
imports: from sympy.utilities.iterables import kbins
label_desc: Use image node_id 1 to create a new CondVariable object  with example: obj = CondVariable(arg, valid)