code: def _pair(x):
      if isinstance(x, collections_abc.Iterable):
          return x
      return x, x
  
file_path: chainer/chainer/functions/pooling/pooling_2d.py
imports: from chainer.backends import cuda
  from chainer import function_node
  from chainer.utils import collections_abc
  from chainer.utils import conv
  from chainer.utils import type_check
label_desc: Use image node_id 1 for calling a global function with example usage: _pair(x) and returns: x,  x, x