On grammatical class:

du'ukau
bridi abstractor: x1 is the answer to the question x2
li'i ze'ei ka
abstractor: experience of being: x1 is x2's experience of being [bridi] (property of x2; with {ce'u} referring to x2's position)
li'i ze'ei nu
abstractor: experience of event: x1 is x2's experience of observing or participating in [bridi] (event)
sedu'u
compound abstractor: sentence/equation abstract; x1 is text expressing [bridi] which is x2.
si'o ze'ei du'u
abstractor: x1 is x2's concept of [bridi] (proposition or {kau}-question)
si'o ze'ei ka
abstractor: x1 is x2's concept of the property [bridi]
si'o ze'ei nu
abstractor: x1 is x2's concept of the event [bridi]
si'o ze'ei poi'i
abstractor: x1 is x2's concept of the object bound to {ke'a} and described by [bridi]