code: static Parser<Expression> compare(Parser<Expression> expr) {
      return Parsers.or(
          compare(expr, ">", Op.GT), compare(expr, ">=", Op.GE),
          compare(expr, "<", Op.LT), compare(expr, "<=", Op.LE),
          compare(expr, "=", Op.EQ), compare(expr, "<>", Op.NE),
          nullCheck(expr), like(expr), between(expr));
    }
docs: ************************ boolean expressions ***************************