mathematical operator: the empty/null [one sense]/trivial [one sense]/blank operator

Arity is context-dependent. Induced structure is /probably/ empty/trivial [one sense] as well.

- gu'ai
- binary operator: left group action g.x
- ma'o'e
- mathematical operator: vague/elliptical/general/generic operator
- ru'ei
- n-ary operator: n-ary magma/group/ring operator a*b = ab`
- sei'au
- terbri editor: passes the terbri value through the quoted function so that the sumti that fills it really is filling the output of the function