docs: def convert_fus(ast):
      """Convert BEL1 fus() to BEL2 fus()"""
  
      parent_fn_name = ast.name_short
      prefix_list = {"p": "p.", "r": "r.", "g": "c."}
      prefix = prefix_list[parent_fn_name]
  
      fus1_ns = ast.args[0].namespace
      fus1_val = ast.args[0].value
  
      arg_fus = ast.args[1]
      fus_args = [None, "?", "?"]
      for idx, arg in enumerate(arg_fus.args):
          fus_args[idx] = arg
  
      fus2_ns = fus_args[0].namespace
      fus2_val = fus_args[0].value
  
      if fus_args[1] == "?":
          fus1_range = fus_args[1]
      else:
          fus1_range = f'"{prefix}1_{fus_args[1].value}"'
  
      if fus_args[2] == "?":
          fus2_range = fus_args[2]
      else:
          fus2_range = f'"{prefix}{fus_args[2].value}_?"'
  
      fus = Function("fus", spec, parent_function=ast)
      fus.args = [
          NSArg(fus1_ns, fus1_val, fus),
          StrArg(fus1_range, fus),
          NSArg(fus2_ns, fus2_val, fus),
          StrArg(fus2_range, fus),
      ]
  
      # Remove BEL
      ast_args = ast.args
      ast_args.pop(0)
      ast_args.pop(0)
  
      if ast_args == [None]:
          ast_args = []
  
      ast.args = []
      ast.add_argument(fus)
  
      if len(ast_args) > 0:
          ast.args.extend(ast_args)
  
      return ast