<0x09> If ▁two ▁nodes ▁have ▁the ▁same ▁label , ▁then ▁their ▁LO ▁or ▁H I ▁edges ▁point ▁to ▁different ▁nodes . ▁In ▁other ▁words , ▁there ▁are ▁no ▁redundant ▁nodes . ▁▁ ▁We ▁call ▁Z ▁an ▁un redu ced ▁Z DD , ▁if ▁a ▁H I ▁edge ▁points ▁to ▁a ▁ ⊥ ▁node ▁or ▁condition ▁ 4 ▁fails ▁to ▁hold . ▁▁ ▁In ▁computer ▁programs , ▁Boolean ▁functions ▁can ▁be ▁expressed ▁in ▁bits , ▁so ▁the ▁ ⊤ ▁node ▁and ▁ ⊥ ▁node ▁can ▁be ▁represented ▁by ▁ 1 ▁and ▁ 0 . ▁From ▁the ▁definition ▁above , ▁we ▁can ▁represent ▁combination ▁sets ▁efficiently ▁by ▁applying ▁two ▁rules ▁to ▁the ▁B DD s : ▁ 1 . E lim inate ▁all ▁the ▁nodes ▁whose ▁ 1 - edge ▁points ▁to ▁the ▁ 0 - term inal ▁node . ▁Then ▁connect ▁the ▁edge ▁to ▁the ▁other ▁sub graph ▁directly , ▁as ▁shown ▁in ▁Figure ▁ 1 . ▁ 2 . Sh are ▁all ▁equivalent ▁sub - graph s ▁the ▁same ▁as ▁for ▁original ▁B DD s . ▁If ▁the ▁number ▁and ▁the ▁order ▁of ▁input ▁variables ▁are ▁fixed , ▁a ▁zero - supp ress ed ▁B DD ▁represents ▁a ▁Boolean ▁function ▁uniqu ely ▁( as ▁proved ▁in ▁Figure ▁ 2 , ▁it ▁is ▁possible ▁to ▁use ▁a ▁B DD ▁to ▁represent ▁a ▁Boolean ▁binary ▁tree ). ▁ ▁Represent ing ▁a ▁family ▁of ▁sets ▁ ▁Let ▁F ▁be ▁a ▁Z DD . ▁Let ▁v ▁be ▁its ▁root ▁node . ▁Then : ▁ 1 . <0x09>