Exortum est in tenebris lumen

Source: 
Sankt Gallen, Stiftsbibliothek, 390
Folio: 
052
Sequence: 
3
Feast: 
Nativitas Domini
Office/Mass: 
V2
Genre: 
A
Position: 
3
Cantus ID: 
002794
Mode: 
7
Differentia: 
yk?
Manuscript Reading Full Text (standardized spelling): 
Exortum est in tenebris lumen rectis corde misericors et miserator et justus dominus
Manuscript Reading Full Text (MS spelling): 
Exortum est in tenebris lumen rectis corde misericors et miserator et iustus dominus
Indexing notes: 
an erased K beside the "y", but is it original?;