This is not a tutorial or explanation. This is just a quick demo on how to isolate the Pentultimate corners. The routine is [6,1] or more specifically [[1:[1,1]],1]. I first do the sequence and then I undo the sequence. As you can see with the Y part you have 4 available corners to put into the spot of the isolated corner so this routine has 4 variations to it by changing only the Y part of the commutator.