This is most welcome and goes in the right direction. A few comments:
- In the first symbol, the “5” should be slashed in the other direction (see Maximvs’ post of May 2021 in this thread).
- Still concerning this symbol, I am not sure that “+6 over /5” means something. But “6 over 5”, “6 over /5”, “+6”, “+6 over 3” are definitely useful.
- The second symbol is useful, but you also need “+7” (plus followed by 7), which means something different. You also need “9 over +” in addition to “7 over +”.
- I would not swear that “+2” and “+3” mean something.
- The two last symbols “+4” and “/7” are definitely useful.
- Note that one also needs a zero (“0”) to express that there is no other voice (for instance, over the bass at the beginning of a fugue).
Looking to an old book published in Switzerland (A. Dommel-Dieny, L’harmonie tonale, 3rd edition, 1963-1973), I also see additional notations such as “+4 over 3” (frequent), “+2 over +4” (rare), “9 over 7 over +” (frequent), “4 over +2”, “3 over +4 over 2”, “5 over +6 over 4”, etc. So, a suitable font should be generic enough to support many combinations.