pro-sumti: a default sumti value for this place in the relationship.
This is not zo'e, but is specifically the default sumti. See also: zo'u'au (non-default but otherwise elliptical sumti), zo'e (elliptical/unspecified sumti, which can be the default), zu'i (typical sumti), zi'o (deleted sumti), di'oi (default sumti, especially according to the selbri's definition), di'au (default sumti, by context and discourse rather than necessarily a selbri's definition), cadyselcu'a (default).