I disagree with his limit on the number of times one can stand up and prostrate again. I believe in 2 and not 3 times for prayer. I don't believe the ruku3 is only a fixed position at the knees, but it can be done like this. It is rather the act of bowing down moving towards prostration. prostration is confirmed by the statement of falling to the chins that we find in the Quran, which is not literal but means falling to the faces and is an Arabic idiom taken from when camels lay down. I also don't believe in a Quran injunction for a friday prayer. the verses speak about going to prayer despite being in times and days of social gathering. I hope this helped.