code: def limit_sub(self):
      localctx = LaTeXParser.Limit_subContext(
          self, self._ctx, self.state
      )
      self.enterRule(localctx, 68, self.RULE_limit_sub)
      self._la = 0  # Token type
      try:
          self.enterOuterAlt(localctx, 1)
          self.state = 469
          self.match(LaTeXParser.UNDERSCORE)
          self.state = 470
          self.match(LaTeXParser.L_BRACE)
          self.state = 471
          _la = self._input.LA(1)
          if not (_la == 77 or _la == 91):
              self._errHandler.recoverInline(self)
          else:
              self._errHandler.reportMatch(self)
              self.consume()
          self.state = 472
          self.match(LaTeXParser.LIM_APPROACH_SYM)
          self.state = 473
          self.expr()
          self.state = 482
          self._errHandler.sync(self)
          _la = self._input.LA(1)
          if _la == 74:
              self.state = 474
              self.match(LaTeXParser.CARET)
              self.state = 480
              self._errHandler.sync(self)
              token = self._input.LA(1)
              if token in [21]:
                  self.state = 475
                  self.match(LaTeXParser.L_BRACE)
                  self.state = 476
                  _la = self._input.LA(1)
                  if not (_la == 15 or _la == 16):
                      self._errHandler.recoverInline(self)
                  else:
                      self._errHandler.reportMatch(self)
                      self.consume()
                  self.state = 477
                  self.match(LaTeXParser.R_BRACE)
                  pass
              elif token in [15]:
                  self.state = 478
                  self.match(LaTeXParser.ADD)
                  pass
              elif token in [16]:
                  self.state = 479
                  self.match(LaTeXParser.SUB)
                  pass
              else:
                  raise NoViableAltException(self)
  
          self.state = 484
          self.match(LaTeXParser.R_BRACE)
      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 36 for calling the LaTeXParser obj's underlying member method code with example usage: obj.limit_sub() and returns: localctx