code: def postfix_op(self):
      localctx = LaTeXParser.Postfix_opContext(
          self, self._ctx, self.state
      )
      self.enterRule(localctx, 22, self.RULE_postfix_op)
      try:
          self.state = 170
          self._errHandler.sync(self)
          token = self._input.LA(1)
          if token in [89]:
              self.enterOuterAlt(localctx, 1)
              self.state = 168
              self.match(LaTeXParser.BANG)
              pass
          elif token in [27]:
              self.enterOuterAlt(localctx, 2)
              self.state = 169
              self.eval_at()
              pass
          else:
              raise NoViableAltException(self)
  
      except RecognitionException as re:
          localctx.exception = re
          self._errHandler.reportError(self, re)
          self._errHandler.recover(self, re)
      finally:
          self.exitRule()
      return localctx
  
imports: from antlr4 import *
  from io import StringIO
  import sys
label_desc: Use image node_id 13 for calling the LaTeXParser obj's underlying member method code with example usage: obj.postfix_op() and returns: localctx