XB-XA->UXA
YB-YA->UYA
XD-XB->UXB
YD-YB->UYB
XA-XC->UXC
YA-YC->UYC
XC-XD->UXD
YC-YD->UYD
~(UYA*XA-(UXA*YA))->CA
~(UYD*XD-(UXD*YD))->CB
YA*XO-(XA*YO)+CA->CA
YD*XO-(XD*YO)+CB->CB
If CAplotdot|E8000=(CBplotdot|E8000)
 Goto CNoColl
End
Text(0,14,"C")
~(UYB*XB-(UXB*YB))->CA
~(UYC*XC-(UXC*YC))->CB
YB*XO-(XB*YO)+CA->CA
YC*XO-(XC*YO)+CB->CB
If CAplotdot|E8000!=(CBplotdot|E8000)
  Goto CColl
End
Lbl CNoColl