Si ambulem in medio umbre mortis
Manuscript P-AR Res. Ms. 16 has two masses for the dead. The missa on folios 180x1r-180x3v appears to be a later addition, it presents simplified melodies and the rubric "Officium defunctorum". The other missa can be read on folios 181r-183r and was originally conceived by the scribe(s) who wrote this source. In the original missa the rubric was not written, however, the selection of chants as well as the comparison with other sources confirms the liturgical occasion.
Chant g00772 is part of the second gradual provided for the original mass for the dead in P-AR Res. Ms. 16. The same gradual appears in the later-added mass, there with the rubric "in anniversario defuncti sequens Responsum".
Chant g00772 is not included the Liber Usualis.