About the lecture on Friday 20th
However, given the multiple requests of changing the lecture, I set up an extra time slot on Wednesday, June 18th to discuss the same exercises sheet (Exercises 4). You can vote for the time slot at http://doodle.com/brgnq3i8u56nhwrc until tomorrow (Tuesday 19th) at 3pm. At that time I will publish the final time for the extra lecture.
To sum up, you can attend to the lecture on Friday June 20th, to the one on Wednesday, June 18th or to both if one time is not enough.