code: def reductionRB(x, f, scope=None):
      """Reduction-B (Fig. 12 and 18 in the v4 paper)"""
      conv1 = conv(x, f[0], 1, scope="3x3a/r")
      conv1 = conv(
          conv1, f[1], 3, stride=2, padding="VALID", scope="3x3a/1"
      )
  
      conv2 = conv(x, f[0], 1, scope="3x3b/r")
      conv2 = conv(
          conv2, f[2], 3, stride=2, padding="VALID", scope="3x3b/1"
      )
  
      conv3 = conv(x, f[0], 1, scope="3x3c/r")
      conv3 = conv(conv3, f[2], 3, scope="3x3c/1")
      conv3 = conv(
          conv3, f[3], 3, stride=2, padding="VALID", scope="3x3c/2"
      )
  
      pool = max_pool2d(x, 3, stride=2, padding="VALID")
  
      x = concat([conv1, conv2, conv3, pool], axis=3, name="concat")
      return x
  
imports: from __future__ import absolute_import
  import tensorflow
  from .layers import avg_pool2d
  from .layers import batch_norm
  from .layers import conv2d
  from .layers import dropout
  from .layers import fc
  from .layers import max_pool2d
  from .layers import sconv2d
  from .layers import convrelu0
  from .layers import convbnrelu
  from .ops import *
  from .utils import pad_info
  from .utils import set_args
  from .utils import var_scope
label_desc: Use image node_id 21 for calling a global function with example usage: reductionRB(x, f, scope) and returns: x