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I was under the impression that whenever you see a mordant or a trill, the auxiliary note is the next note up in the key signature.
But I'm a bit confused on how to proceed here. This is measure 57 of the first movement of Beethoven's Eighth Piano Sonata in C Minor (the piece is in common time).
(The measure uses the treble clef). The first mordant seems simple enough: I play a G-flat, I briefly brush a whole step up to the A-flat (since A-flat comes after G in the key of C Minor), hold the G-flat for the rest of the note's duration, and then play the F in the third beat.
But what about the second mordant? What's the auxiliary note? Normally, it'd be a G-natural, since in C Minor G-natural follows the F, but that accidental on the G-flat earlier in the measure is confusing me. Does it carry over to the auxiliary note on the second mordant? For the third beat in the measure, do I play F—G-flat—F or F—G—F?