ocr: 4.43. Now wC understand that the cross-section of the band is not an inter- val. It must be a: folded interval with two Jayers, Let's follow the evolucion of thia folded interval as. il guesi aroun, répeal- ing exaculy the steps above. Starting another Lumn as al-shaped channel, the stretch and fold woduccs a deuble-U- shape on relurn to lhe Poincaresetion.