code: def TR7(rv):
      """Lowering the degree of cos(x)**2.
  
      Examples
      ========
  
      >>> from sympy.simplify.fu import TR7
      >>> from sympy.abc import x
      >>> from sympy import cos
      >>> TR7(cos(x)**2)
      cos(2*x)/2 + 1/2
      >>> TR7(cos(x)**2 + 1)
      cos(2*x)/2 + 3/2
  
      """
  
      def f(rv):
          if not (rv.is_Pow and rv.base.func == cos and rv.exp == 2):
              return rv
          return (1 + cos(2 * rv.base.args[0])) / 2
  
      return bottom_up(rv, f)
  
imports: from collections import defaultdict
  from sympy.core.add import Add
  from sympy.core.expr import Expr
  from sympy.core.exprtools import Factors, gcd_terms, factor_terms
  from sympy.core.function import expand_mul
  from sympy.core.mul import Mul
  from sympy.core.numbers import pi, I
  from sympy.core.power import Pow
  from sympy.core.singleton import S
  from sympy.core.sorting import ordered
  from sympy.core.symbol import Dummy
  from sympy.core.sympify import sympify
  from sympy.core.traversal import bottom_up
  from sympy.functions.combinatorial.factorials import binomial
  from sympy.functions.elementary.hyperbolic import cosh, sinh, tanh, coth, sech, csch, HyperbolicFunction
  from sympy.functions.elementary.trigonometric import cos, sin, tan, cot, sec, csc, sqrt, TrigonometricFunction
  from sympy.ntheory.factor_ import perfect_power
  from sympy.polys.polytools import factor
  from sympy.strategies.tree import greedy
  from sympy.strategies.core import identity, debug
  from sympy import SYMPY_DEBUG
label_desc: Use image node_id 10 for calling a global function with example usage: TR7(rv) and returns: bottom_up, unknown, rv