+-+ | | + + +-+ | | /| | +--+--+ +--+--+ + + | | |\ + | + +--+ + v| x | /| / +--+ + + + + a<-+--+ | | | \ ^ | + b + \ | | | ^ | \ | | + | +--+--+ \| | \| \ Hoan a | + 1 Dor | |\ | | \ +-----------+--+--+--+--+--+ | \| | | | | | +-+ + + + + v +--+--+--+--+--b--+--+->+