code: def eval_at(self):
      localctx = LaTeXParser.Eval_atContext(self, self._ctx, self.state)
      self.enterRule(localctx, 24, self.RULE_eval_at)
      try:
          self.enterOuterAlt(localctx, 1)
          self.state = 172
          self.match(LaTeXParser.BAR)
          self.state = 178
          self._errHandler.sync(self)
          la_ = self._interp.adaptivePredict(self._input, 11, self._ctx)
          if la_ == 1:
              self.state = 173
              self.eval_at_sup()
              pass
  
          elif la_ == 2:
              self.state = 174
              self.eval_at_sub()
              pass
  
          elif la_ == 3:
              self.state = 175
              self.eval_at_sup()
              self.state = 176
              self.eval_at_sub()
              pass
  
      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 14 for calling the LaTeXParser obj's underlying member method code with example usage: obj.eval_at() and returns: localctx