- Supp ress ed ▁Dec ision ▁Di agram ▁( Z DD ) ▁ ▁to ▁be ▁any ▁directed ▁a cyc lic ▁graph ▁such ▁that : ▁▁ 1 . <0x09> A ▁terminal ▁node ▁is ▁either : ▁▁ <0x09> The ▁special ▁ ⊤ ▁node ▁ ▁( the ▁TRUE ▁node ), ▁or : ▁ <0x09> The ▁special ▁ ⊥ ▁node ▁ ▁( the ▁FALSE ▁node ). ▁ 2 . <0x09> Each ▁non term inal ▁node ▁satisfies ▁the ▁following ▁conditions : ▁a . <0x09> The ▁node ▁is ▁label led ▁with ▁a ▁positive ▁integer ▁v . ▁This ▁label ▁does ▁not ▁have ▁to ▁be ▁unique . ▁ ▁b . <0x09> The ▁node ▁has ▁an ▁out - deg ree ▁of ▁ 2 . ▁One ▁of ▁the ▁out going ▁edges ▁is ▁named ▁“ LO ”, ▁and ▁the ▁other ▁“ HI ”. ▁( In ▁diag rams , ▁one ▁may ▁draw ▁d otted ▁lines ▁for ▁LO ▁edges ▁and ▁solid ▁lines ▁for ▁H I ▁edges ) ▁c . <0x09> A ▁destination ▁node ▁is ▁either ▁terminal ▁or ▁label led ▁with ▁an ▁integer ▁strictly ▁larger ▁than ▁v . ▁Thus ▁one ▁can ▁o mit ▁arrow head s ▁in ▁diag rams ▁because ▁the ▁edge ▁directions ▁can ▁be ▁infer red ▁form ▁the ▁labels . ▁ ▁d . <0x09> The ▁H I ▁edge ▁never ▁points ▁to ▁the ▁ ⊥ ▁node . ▁▁ 3 . <0x09> There ▁is ▁exactly ▁one ▁node ▁with ▁zero ▁in - deg ree — the ▁root ▁node . ▁The ▁root ▁node ▁is ▁either ▁terminal ▁or ▁label led ▁by ▁the ▁smallest ▁integer ▁in ▁the ▁diagram . ▁ 4 .