ORAL JUDGMENT :- Rule. Rule made returnable forthwith and is heard by consent. 2. According to the petitioner/management : (a) The petitioner was appointed for the first time on 20-6-1994, the post was meant for reserved category candidate, however, the management did not mention the said fact in the appointment order. (b) After completion of two year's service, the petitioner was issued a fresh appointment order dated 24-6-1996, which admittedly mentions that this time, he is given appointment on probation of two years against a reserved vacancy. 3. After termination, the petitioner preferred Appeal No. 202/1998, which was delayed by 7 months. Petitioner claimed that he had gained permanency and claimed the relief of reinstatement and backwages alleging that the termination is illegal. 4. The appeal was opposed urging inter alia that : (1) as the post was reserved there cannot be any permanent appointment of an open category candidate against a vacancy meant for candidate belonging to particular category of reservation and therefore an order of reinstatement on such post of a candidate who was appointed against such reserved vacancy is also impermissible; and (2) when a candidate is appointed on a post reserved for any particular category and accepts the order of appointment on vacancy of the said nature, such appointee is estopped from taking the plea that the post was not reserved or that he has gained permanency and also from contending that the order of appointment was not proper etc. 5. Learned Advocate Mr. S. R. Barlinge, has placed reliance on the judgment of this Court reported in 2007(6) Mh.L.J. 847 , between Kini Karyat Shikshan Mandai and another vs. Pramod Satuppa Oulkar and others, to urge - the point of estoppel. 6. Insofar as 1st point as to unaffected character of vacancy meant for reserved category is concerned there cannot be two opinions on it. Its applicability will however depend on the proof of fact as to nature of vacancy being reserved for any particular category. 7. As far as second point is concerned, it is well settled that 'estoppel' is a rule of evidence. This rule recognizes a right accrued to a party when due to conduct of former, later party is placed in a advantageous position due to acts and representations of the former. 7. As far as second point is concerned, it is well settled that 'estoppel' is a rule of evidence. This rule recognizes a right accrued to a party when due to conduct of former, later party is placed in a advantageous position due to acts and representations of the former. The right so accrued that the former party so acting would not be entitled to retract as such conduct shall drag later to a disadvantageous position. This basic doctrine of estoppel does not need any further elucidation and further support of precedent. 8. The question which arises is whether on facts, has the conduct of employee put the management in such position, that a contrary stand by employee would put the management in a disadvantageous position, and therefore now the employee should not be allowed to retract and thereby prejudice the employer. This aspect will have to be ruled upon after taking entire resume of facts, which however need not be repeated and it shall suffice to refer to para 2 in the beginning. 9. The best evidence of fact of post being reserved is of document i.e. roster which is a document required to be maintained by the management and to be approved by Government Officers who are vested with the powers and duty of achieving the object of ensuring the due and proper reservation as mandated by the Constitution of India and translated into rules under the Act in question. 10. It is obligatory on the part of every management to maintain the roster to enable it to ensure the reservation and then to fill in the vacancies according to the order of reservation indicated therein. The management/petitioner was bound to keep in own possession the said roster. Without possession of such roster, it would be impossible for the management to plead that a particular vacancy, as alleged in the present case, was meant to be filled by a candidate of a particular category of reservation. 11. The roster to be so maintained has to be not just best but only evidence for proof of fact of reservation. The petitioner has refrained from bringing on record the said original roster which• is expected to be duly certified by the Government authorities. 12. After withholding and suppressing its own record from the Court, now the petitioner is advancing a plea of estoppel against the respondent. 13. The petitioner has refrained from bringing on record the said original roster which• is expected to be duly certified by the Government authorities. 12. After withholding and suppressing its own record from the Court, now the petitioner is advancing a plea of estoppel against the respondent. 13. The petitioner has thus withheld best evidence and desires that initially the Tribunal, should have accepted their word that the post was reserved and now wants this Court to do it. 14. In this background the Tribunal has perused the record and has found that the approval orders which were brought on record did not contain a mention or stipulation that the approval was against a reserved vacancy. Tribunal has also noticed that the roster which was to be the best evidence of reservation was not produced. 15. This fact that the vacancy was reserved is required to be proved by primary evidence to be brought by the management. A party withholding from the could best evidence has to suffer its adverse inference. Proof of facts by primary evidence cannot be dispensed with by relying upon cruches of stretched argument of rule estoppel which too is not well founded. 16. The fact which was jurisdictional and pivotal is, as to whether vacancy in question was a reserved vacancy and the petitioners have failed to discharge their burden. It is therefore liable to be held that the post on which respondent employee was appointed was not a vacancy meant for a candidate of reserved category. 17. In this background, the judgment of the School Tribunal which is based on record is not shown to be erroneous much less perverse. The impugned judgment and order therefore does not call for interference. 18. Rule is discharged with costs. Petition dismissed.