code: def _tgrep_node_label_pred_use_action(_s, _l, tokens):
      """
      Builds a lambda function representing a predicate on a tree node
      which describes the use of a previously bound node label.
  
      Called for expressions like (`tgrep_node_label_use_pred`)::
  
          =s
  
      when they appear inside a tgrep_node_expr (for example, inside a
      relation).  The predicate returns true if and only if its node
      argument is identical the the node looked up in the node label
      dictionary using the node's label.
      """
      assert len(tokens) == 1
      assert tokens[0].startswith("=")
      node_label = tokens[0][1:]
  
      def node_label_use_pred(n, m=None, l=None):
          # look up the bound node using its label
          if l is None or node_label not in l:
              raise TgrepException(
                  f"node_label ={node_label} not bound in pattern"
              )
          node = l[node_label]
          # truth means the given node is this node
          return n is node
  
      return node_label_use_pred
  
imports: import functools
  import re
  import nltk.tree
label_desc: Use image node_id 21 for calling a global function with example usage: _tgrep_node_label_pred_use_action(_s, _l, tokens) and returns: node_label_use_pred, unknown