code: def checkASN(filename):
      
      # Extract the file extn type:
      extnType = filename[filename.rfind('_')+1:filename.rfind('.')]
  
      # Determine if this extn name is valid for an assocation file
      if isValidAssocExtn(extnType):
          return True
      else:
          return False
docs: Determine if the filename provided to the function belongs to
      an association.
  
      Parameters
      ----------
      filename: string
  
      Returns
      -------
      validASN  : boolean value