This is makeindex, version 2.15 [TeX Live 2018/W32TeX] (kpathsea + Thai support).
Scanning input file GradualeMonasterienseParsTertia-Intr.idx....done (1 entries accepted, 0 rejected).
Sorting entries...done (0 comparisons).
Generating output file GradualeMonasterienseParsTertia-Intr.ind....done (5 lines written, 0 warnings).
Output written in GradualeMonasterienseParsTertia-Intr.ind.
Transcript written in GradualeMonasterienseParsTertia-Intr.ilg.