In Indra Sawhney vs. Union of India [1992 Supp.(3) SCC 217], the principle of horizontal reservation was explained thus (Pr.812) :
"all reservations are not of the same nature. There are two types of reservations, which may, for the sake of convenience, be referred to as 'vertical reservations’ and 'horizontal reservations’. The reservations in favour of Scheduled Castes, Scheduled Tribes and Other Backward Classes [(under Article 16(4)] may be called vertical reservations whereas reservations in favour of physically handicapped (under clause (1) of Article 16] can be referred to as horizontal reservations. Horizontal reservations cut across the vertical reservations - what is called interlocking reservations. To be more precise, suppose 3% of the vacancies are reserved in favour of physically handicapped persons; this would be a reservation relatable to clause (1) of Article 16. The persons selected against the quota will be placed in that quota by making necessary adjustments; similarly, if he belongs to open competition (OC) category, he will be placed in that category by making necessary adjustments. Even after providing for these horizontal reservations, the percentage of reservations in favour of backward class of citizens remains - and should remain - the same."
2) The method of implementing special reservation, which is a horizontal reservation, cutting across vertical reservations, was explained by this Court in Anil Kumar Gupta vs. State of U.P. [1995 (5) SCC 173] thus :
"The proper and correct course is to first fill up the Open Competition quota (50%) on the basis of merit; then fill up each of the social reservation quotas, i.e., S.C., S.T. and B.C; the third step would be to find out how many candidates belonging to special reservations have been selected on the above basis. If the quota fixed for horizontal reservations is already satisfied - in case it is an overall horizontal reservation - no further question arises. But if it is not so satisfied, the requisite number of special reservation candidates shall have to be taken and adjusted/accommodated against their respective social reservation categories by deleting the corresponding number of candidates therefrom. (If, however, it is a case of compartmentalized horizontal reservation, then the process of verification and adjustment/accommodation as stated above should be applied separately to each of the vertical reservations. In such a case, the reservation of fifteen percent in favour of special categories, overall, may be satisfied or may not be satisfied.)
3) in the vent you are aggrieved by policy of dept in not considering the Sc judgment file writ petition in HC to challenge the selection process