In Debussy's La Fille aux Cheveux de Lin, there is this passage:
(Debussy: Préludes Livre I, No. 8, bar 24) The piece is in Gb major.
This first chord is probably a I chord. But since it has that extra Eb, does it mean it's a I13 chord, despite the fact it has no other notes from that extension? Or is it just a normal I chord with some decoration?
The other option is that it's vi7b chord. Is this more likely?