So, I'm supposed to play for a Las Posadas (a Mexican Christmas service) on Sunday and I look at the music last night. Everything is in D (2 sharps) and so far so good. I look a the chord markings above the staff and they read "Re", "Sol", "La7". I'm thinking, OK it's do, re, mi, fa, sol, la, ti, do. So maybe the "translation" is Re = Em (ii chord), Sol = A (V chord), and La7 = Bm7 (vi chord). Then I look at the melody line and it's clear that's not right. Where I thought I'd play an Em, the melody notes are A, F#, D and it's the same for the others. Can anyone enlighten this gringo? 
Ron

Ron