It's on bar 17, including the anacrusis, between the second A sharp and the G one octave higher.
Uuuhhhmm... Prelude No 20 is only 13 bars long... I think you've got the wrong number!Edit: I've found it. What you mean is Prelude No 4 (!!!) op 28, bar 16.If I'm not mistaken, stretta means that you play faster. I don't know what to do with the ornament, though...
The Presto con fuoco isn't as hard as it looks. There are many patterns to the passages.Slow practice /wout pedal to build up accuracy and then speed it up gradually.My teacher from a while ago suggested crawling of the fingers of the right hand, but I prefer lifting the hand very much and settling it down, it provids more clarity.What presto con fuoco? Not talking about the fourth etude here...