class_docstr: A little class to represent an interior node in the tree
  
  This is analogous to SymPy.Basic for non-Atoms
code: def __init__(self, op, args):
      self.op = op
      self.args = args
  
imports: from sympy.utilities.iterables import kbins
label_desc: Use image node_id 1 to create a new Compound object  with example: obj = Compound(op, args)