code: def reduce_mean_over_bl_sum_over_c(x, x_mask):
      """Returns mean of x over B and L and sum over C."""
      mean = reduce_mean_over_bl(x, x_mask)
      return tf.reduce_sum(mean)
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import copy
  import math
  from tensor2tensor.layers import common_attention
  from tensor2tensor.layers import common_layers
  from tensor2tensor.models.transformer import transformer_decoder_layer
  import tensorflow.compat.v1
  import tensorflow_probability
label_desc: Use image node_id 9 for calling a global function with example usage: reduce_mean_over_bl_sum_over_c(x, x_mask) and returns: tf