code: def unpack(expr):
      """Rule to unpack singleton args
  
      >>> from sympy.strategies import unpack
      >>> from sympy import Basic, S
      >>> unpack(Basic(S(2)))
      2
      """
      if len(expr.args) == 1:
          return expr.args[0]
      else:
          return expr
  
file_path: sympy/sympy/strategies/rl.py
imports: from sympy.utilities.iterables import sift
  from .util import new
label_desc: Use image node_id 6 for calling a global function with example usage: unpack(expr) and returns: expr, expr