convert number into pro-sumti: definitional terbri variable with associated number; x_{n}

Extends bo'a series indefinitely.

- cei'e
*(exp!)* - define following selbri with sentence or tu'e...tu'u clause
- ka'ei
*(exp!)* - abstractor: predicate abstractor. x
_{1}is the predicate expressed by [bridi], using bo'a, bo'e, etc for variables. - kai'ei
*(exp!)* - abstractor: x
_{1}(x_{2}, ...) are such that they satisfy [bridi], using bo'a/bo'e/etc for variables