▁Men ng ag de ▁teach ings ▁to ▁Tib et ▁in ▁the ▁ 8 th ▁Century . ▁▁ ▁The ▁G loss ary ▁for ▁Rang j ung ▁Yes he ▁books ▁described ▁men ng ak de : ▁ ▁The ▁three ▁series ▁do ▁not ▁represent ▁different ▁schools ▁of ▁D z og chen ▁practice ▁as ▁much ▁as ▁different ▁approaches . ▁As ▁is ▁common ▁throughout ▁much ▁Buddh ist ▁literature , ▁Tib et an ▁Buddh ism ▁in ▁particular , ▁the ▁divisions ▁are ▁sometimes ▁said ▁to ▁represent ▁grad ations ▁in ▁the ▁fac ult ies ▁of ▁the ▁students ▁for ▁whom ▁the ▁practices ▁are ▁appropriate ; ▁pract ition ers ▁of ▁low , ▁m idd ling , ▁and ▁high ▁fac ult ies , ▁respectively . ▁ ▁Dist ingu ishing ▁Fe atures ▁of ▁the ▁Men ng ag de ▁( O ral ▁Inst ruction ▁Series ) ▁The ▁distingu ishing ▁features ▁of ▁Men ng ag de ▁are ▁the ▁practices ▁of ▁l h ünd rup ▁t ög al ▁and ▁k ad ak ▁tre k ch ö . ▁ ▁Another ▁feature ▁of ▁the ▁men ng ag de ▁is ▁the ▁s ā d han ā ▁of ▁the ▁Seven ▁Mind ▁Train ings ▁() ▁Cap ril es ▁( 2 0 0 3 : ▁p .   1 0 3 ) ▁ident ifies ▁the ▁s ā d han ā ▁of ▁the ▁" Se ven ▁L oj ong ". ▁ ▁Four ▁divisions ▁of ▁Men ng ag de ▁Men ng ag de ▁itself ▁is ▁sometimes ▁said ▁to ▁have ▁been ▁further ▁divided ▁by ▁Sri ▁Sing ha ▁into ▁four ▁categories , ▁called ▁the ▁" F our ▁Cy