▁Every ▁job ▁must ▁complete ▁before ▁its ▁dead line . ▁ ▁p mt n ▁ ▁Job s ▁can ▁be ▁pre empt ed ▁and ▁res umed ▁possibly ▁on ▁another ▁machine . ▁Sometimes ▁also ▁denoted ▁by ▁' pr mp '. ▁▁▁ ▁Each ▁job ▁comes ▁with ▁a ▁number ▁of ▁machines ▁on ▁which ▁it ▁must ▁be ▁scheduled ▁at ▁the ▁same ▁time , ▁default ▁is ▁ 1 . ▁ ▁Pre ced ence ▁relations ▁▁ ▁Pre ced ence ▁relations ▁might ▁be ▁given ▁for ▁the ▁jobs , ▁in ▁form ▁of ▁a ▁partial ▁order , ▁meaning ▁that ▁if ▁i ▁is ▁a ▁prede cess or ▁of ▁i ' ▁in ▁that ▁order , ▁i ' ▁can ▁start ▁only ▁when ▁i ▁is ▁completed . ▁▁ ▁prec ▁ ▁Given ▁general ▁preced ence ▁relation . ▁ ▁If ▁ ▁then ▁starting ▁time ▁of ▁ ▁should ▁be ▁not ▁earlier ▁than ▁completion ▁time ▁of ▁. ▁ ▁ch ains ▁ ▁Given ▁preced ence ▁relation ▁in ▁form ▁of ▁ch ains ▁( inde gre es ▁and ▁out de gre es ▁are ▁at ▁most ▁ 1 ). ▁ ▁tree ▁ ▁Given ▁general ▁preced ence ▁relation ▁in ▁form ▁of ▁a ▁tree , ▁either ▁int ree ▁or ▁out tree . ▁ ▁int ree ▁ ▁Given ▁general ▁preced ence ▁relation ▁in ▁form ▁of ▁an ▁int ree ▁( out de gre es ▁are ▁at ▁most ▁ 1 ). ▁ ▁out tree ▁ ▁Given ▁general ▁preced ence ▁relation ▁in ▁form ▁of ▁an ▁out tree ▁( inde gre es ▁are ▁at ▁most ▁ 1 ). ▁ ▁oppos ing ▁forest ▁ ▁Given ▁general ▁preced ence ▁relation ▁in ▁form ▁of ▁a ▁collection