code: def sub(a, b):
      """Elementwise subtracts two blobs or a blob and a scalar value."""
      if not type(a) is Blob and not type(b) is Blob:
          raise ValueError(
              "At least one of `a` and `b` should be neoml.Blob."
          )
  
      return a - b
  
imports: import neoml
  import neoml.PythonWrapper
  from neoml.MathEngine import MathEngine
  from neoml.Blob import Blob
  import numpy
label_desc: Use image node_id 3 for calling a global function with example usage: sub(a, b) and returns: unknown