iew icz ▁bound . ▁Cl osing ▁the ▁gap ▁between ▁this ▁lower ▁bound ▁and ▁the ▁upper ▁bound ▁remains ▁an ▁open ▁problem . ▁ ▁Rect il ine ar ▁crossing ▁numbers ▁If ▁edges ▁are ▁required ▁to ▁be ▁drawn ▁as ▁straight ▁line ▁segments , ▁rather ▁than ▁arbitrary ▁curves , ▁then ▁some ▁graphs ▁need ▁more ▁cross ings ▁than ▁they ▁would ▁when ▁drawn ▁with ▁cur ved ▁edges . ▁However , ▁the ▁upper ▁bound ▁established ▁by ▁Zar ank iew icz ▁for ▁the ▁crossing ▁numbers ▁of ▁complete ▁b ipart ite ▁graphs ▁can ▁be ▁achieved ▁using ▁only ▁straight ▁edges . ▁Therefore , ▁if ▁the ▁Zar ank iew icz ▁conject ure ▁is ▁correct , ▁then ▁the ▁complete ▁b ipart ite ▁graphs ▁have ▁rect il ine ar ▁crossing ▁numbers ▁equal ▁to ▁their ▁crossing ▁numbers . ▁ ▁References ▁ ▁External ▁links ▁ ▁Category : Top ological ▁graph ▁theory ▁Category : Graph ▁drawing ▁Category : Math emat ical ▁problems ▁Category : Con ject ures ▁Category : Uns ol ved ▁problems ▁in ▁mathematics <0x0A> </s> ▁The ▁WCF ▁& ▁N ▁Center ▁Point ▁Dep ot ▁and ▁Sub station , ▁also ▁known ▁as ▁the ▁Center ▁Point ▁Dep ot ▁Museum , ▁is ▁a ▁historic ▁building ▁located ▁in ▁Center ▁Point , ▁Iowa , ▁United ▁States . ▁ ▁The ▁Mission ▁Rev ival ▁building ▁was ▁constructed ▁in ▁ 1 9 1 4 ▁by ▁the ▁Water lo o , ▁C ed ar ▁F alls ▁and ▁Northern ▁Rail road , ▁an ▁inter urban ▁line ▁that ▁ran ▁between ▁the ▁Water lo o ▁– ▁C ed ar ▁F alls ▁area ▁and ▁C ed ar ▁Rap ids . ▁Pass