I'm looking at the Henle edition of Bach's WTC, specifically at d-moll Fugue (BWV 851), and in the second measure I see a trill:
(This is András Schiff's fingering). What is that horizontal bar over numbers 3 and 2 supposed to mean? I guess, Schiff means here something like what is described in this answer (see Option 1), namely, play A with 3rd finger, then G with 2nd finger, iterate this for some time (and this is what the bar actually means), and then go to F with 1st finger, and again G with 2nd. But I am not sure (partly because this notation does not give specific notes, but the fingers only). So,
- Am I right in my conclusion that the bar means "repeat these two notes for some time"?
- A meta-question: how was I supposed to know this? Is it in some (or every) piano textbook and everyone just learns it in fourth grade or something? Is there a canonical source of widely accepted notation regarding fingering in the modern piano literature, or in Henle editions in particular? By the way, my edition includes "Table of ornaments", which shows how to play various "idems" and "Doppelt-Cadences", but it does not mention a common trill, and my guess looks more like "Trillo und Mordant" in this table.