code: def cse_release_variables(r, e):
      """
      Return tuples giving ``(a, b)`` where ``a`` is a symbol and ``b`` is
      either an expression or None. The value of None is used when a
      symbol is no longer needed for subsequent expressions.
  
      Use of such output can reduce the memory footprint of lambdified
      expressions that contain large, repeated subexpressions.
  
      Examples
      ========
  
      >>> from sympy import cse
      >>> from sympy.simplify.cse_main import cse_release_variables
      >>> from sympy.abc import x, y
      >>> eqs = [(x + y - 1)**2, x, x + y, (x + y)/(2*x + 1) + (x + y - 1)**2, (2*x + 1)**(x + y)]
      >>> defs, rvs = cse_release_variables(*cse(eqs))
      >>> for i in defs:
      ...   print(i)
      ...
      (x0, x + y)
      (x1, (x0 - 1)**2)
      (x2, 2*x + 1)
      (_3, x0/x2 + x1)
      (_4, x2**x0)
      (x2, None)
      (_0, x1)
      (x1, None)
      (_2, x0)
      (x0, None)
      (_1, x)
      >>> print(rvs)
      (_0, _1, _2, _3, _4)
      """
      if not r:
          return r, e
  
      s, p = zip(*r)
      esyms = symbols("_:%d" % len(e))
      syms = list(esyms)
      s = list(s)
      in_use = set(s)
      p = list(p)
      # sort e so those with most sub-expressions appear first
      e = [(e[i], syms[i]) for i in range(len(e))]
      e, syms = zip(
          *sorted(
              e,
              key=lambda x: -sum(
                  [
                      p[s.index(i)].count_ops()
                      for i in x[0].free_symbols & in_use
                  ]
              ),
          )
      )
      syms = list(syms)
      p += e
      rv = []
      i = len(p) - 1
      while i >= 0:
          _p = p.pop()
          c = in_use & _p.free_symbols
          if c:  # sorting for canonical results
              rv.extend([(s, None) for s in sorted(c, key=str)])
          if i >= len(r):
              rv.append((syms.pop(), _p))
          else:
              rv.append((s[i], _p))
          in_use -= c
          i -= 1
      rv.reverse()
      return rv, esyms
  
imports: from collections import defaultdict
  from sympy.core import Basic, Mul, Add, Pow, sympify
  from sympy.core.containers import Tuple, OrderedSet
  from sympy.core.exprtools import factor_terms
  from sympy.core.singleton import S
  from sympy.core.sorting import ordered
  from sympy.core.symbol import symbols, Symbol
  from sympy.matrices import MatrixBase, Matrix, ImmutableMatrix, SparseMatrix, ImmutableSparseMatrix
  from sympy.matrices.expressions import MatrixExpr, MatrixSymbol, MatMul, MatAdd, MatPow, Inverse
  from sympy.matrices.expressions.matexpr import MatrixElement
  from sympy.polys.rootoftools import RootOf
  from sympy.utilities.iterables import numbered_symbols, sift, topological_sort, iterable
  from .None import cse_opts
label_desc: Use image node_id 3 for calling a global function with example usage: cse_release_variables(r, e) and returns: rv,  esyms, r,  e