code: def abs_group(self):
      localctx = LaTeXParser.Abs_groupContext(
          self, self._ctx, self.state
      )
      self.enterRule(localctx, 40, self.RULE_abs_group)
      try:
          self.enterOuterAlt(localctx, 1)
          self.state = 269
          self.match(LaTeXParser.BAR)
          self.state = 270
          self.expr()
          self.state = 271
          self.match(LaTeXParser.BAR)
      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 22 for calling the LaTeXParser obj's underlying member method code with example usage: obj.abs_group() and returns: localctx