It's just a subdivision; it might as well have said 1a, 1b... -- but "bis" and "...

schoen · on Oct 13, 2021

It should normally be "bis" and "ter".

The Latin for "once, twice, thrice, four times, five times" is "semel, bis, ter, quater, quinquies". ("Bis" and "ter" are the only really short ones.)

It's moderately common in European standards and bureaucracy to use "bis" and "ter" for "version/revision 2" and "version/revision 3", respectively. For example https://en.wikipedia.org/wiki/List_of_ITU-T_V-series_recomme...

lvh · on Oct 13, 2021

Huh, good point; I wonder if my mind mixed up the org chem with the numbers (likely) or if that's some kind of unique Belgian affectation.

whoisburbansky · on Oct 12, 2021

Ah, gotcha. I thought I recognized the prefixes from Organic, but I don't think I've seen it used like this here. Neat!