code: def difference_delta(expr, n=None, step=1):
      """Difference Operator.
  
      Explanation
      ===========
  
      Discrete analog of differential operator. Given a sequence x[n],
      returns the sequence x[n + step] - x[n].
  
      Examples
      ========
  
      >>> from sympy import difference_delta as dd
      >>> from sympy.abc import n
      >>> dd(n*(n + 1), n)
      2*n + 2
      >>> dd(n*(n + 1), n, 2)
      4*n + 6
  
      References
      ==========
  
      .. [1] https://reference.wolfram.com/language/ref/DifferenceDelta.html
      """
      expr = sympify(expr)
  
      if n is None:
          f = expr.free_symbols
          if len(f) == 1:
              n = f.pop()
          elif len(f) == 0:
              return S.Zero
          else:
              raise ValueError(
                  "Since there is more than one variable in the"
                  " expression, a variable must be supplied to"
                  " take the difference of %s" % expr
              )
      step = sympify(step)
      if step.is_number is False or step.is_finite is False:
          raise ValueError("Step should be a finite number.")
  
      if hasattr(expr, "_eval_difference_delta"):
          result = expr._eval_difference_delta(n, step)
          if result:
              return result
  
      return expr.subs(n, n + step) - expr
  
file_path: sympy/sympy/series/limitseq.py
imports: from sympy.calculus.accumulationbounds import AccumulationBounds
  from sympy.core.add import Add
  from sympy.core.function import PoleError
  from sympy.core.power import Pow
  from sympy.core.singleton import S
  from sympy.core.symbol import Dummy
  from sympy.core.sympify import sympify
  from sympy.functions.combinatorial.numbers import fibonacci
  from sympy.functions.combinatorial.factorials import factorial, subfactorial
  from sympy.functions.special.gamma_functions import gamma
  from sympy.functions.elementary.complexes import Abs
  from sympy.functions.elementary.miscellaneous import Max, Min
  from sympy.functions.elementary.trigonometric import cos, sin
  from sympy.series.limits import Limit
label_desc: Use image node_id 1 for calling a global function with example usage: difference_delta(expr, n, step) and returns: unknown, result, S