I'm stuck again, this time in Testchamber 19 in Chapter 4.
I've used the cubicle on the ground to change the angle of the laser on the right. I also know there's are cubicles to the left and right of where you enter Testchamber 19.
But I couldn't find a way to make use of Portals to get to get to those cubicles. So any hints as to what I should do next?