abstractor: predicate abstractor. x1 is the predicate expressed by [bridi], using bo'a, bo'e, etc for variables.
Identical in meaning to an n-ary ka, but with lambda-variables bound to bo'a/bo'e/bo'i/bo'o/bo'u (bo'ai for additional variables) instead of ce'u (which may still be used for "next place"). This is mainly for convenience, to avoid having to assign pro-sumti to ce'u variables either with goi or ce'ai. See me'ei, me'au, cei'e, ckaji, ckini