[lojban] zi, vi, ca, bu'u

[Gregory Dyke <lojban-out@lojban.org>]

I've been sort of reading over the phpbb, and I'm trying to get clear 
what the cmavo in the subject line should be used for.

First: Am I correct in saying that zi is the time equivalent of vi? and 
that ca is the time equivalent of bu'u?

On irc, I said: ma nuzba vi le norge (the example xorxes quotes on phpbb)

Is this incorrect or just not as accurate as it should be? What would be 
a less "foreign" way of saying this?

ma nuzba ne'i le norge
ma nuzba bu'u le norge
...

What exactly does bu'u mean? Pragmatically, two objects cannot occupy 
the same space: I can be in something, around something, but not 
coincident with something.

Usage tends to favour {ca} in such sentences as "mi klama ca le cabdei", 
but {vi} in "mi citka vi la bastn"

These two sentences contain virtually the same information, one about 
time, the other about space. And yet one uses {vi} and the other {ca}.

I'd have thought they should be using equivalent tenses: "mi klama zi le 
cabdei" or "mi citka bu'u la bastn"

Which is it?