This is makeindex, version 2.15 [TeX Live 2017] (kpathsea + Thai support).
Scanning input file refman.idx....done (273 entries accepted, 0 rejected).
Sorting entries.....done (2408 comparisons).
Generating output file refman.ind....done (412 lines written, 0 warnings).
Output written in refman.ind.
Transcript written in refman.ilg.
