code: def TR4(rv):
      """Identify values of special angles.
  
          a=  0   pi/6        pi/4        pi/3        pi/2
      ----------------------------------------------------
      sin(a)  0   1/2         sqrt(2)/2   sqrt(3)/2   1
      cos(a)  1   sqrt(3)/2   sqrt(2)/2   1/2         0
      tan(a)  0   sqt(3)/3    1           sqrt(3)     --
  
      Examples
      ========
  
      >>> from sympy import pi
      >>> from sympy import cos, sin, tan, cot
      >>> for s in (0, pi/6, pi/4, pi/3, pi/2):
      ...    print('%s %s %s %s' % (cos(s), sin(s), tan(s), cot(s)))
      ...
      1 0 0 zoo
      sqrt(3)/2 1/2 sqrt(3)/3 sqrt(3)
      sqrt(2)/2 sqrt(2)/2 1 1
      1/2 sqrt(3)/2 sqrt(3) sqrt(3)/3
      0 1 zoo 0
      """
      # special values at 0, pi/6, pi/4, pi/3, pi/2 already handled
      return rv
  
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 6 for calling a global function with example usage: TR4(rv) and returns: rv