Huh, weird. It makes sense for non-count things. All water flows downhill.
((Ĉiu, singular, by the way, implies either a non-countable substance (water, air, ...) or that a countable group (people, ...) does things individually. This is similar to the each/all distinction in English, except that Esperanto uses ĉiu more often than English uses each. "Ĉiuj devas morti" sounds a lot like an order to "kill them all now."))
Somewhere I got it into my head that "ĉiu" means "each" (like "each apple gives nutrition," etc) and that to address "everyone" (as in people or listeners), one should say "ĉiuj."
Yes, I think that's pretty close to the truth. Another way to look at it:
- ĉiu - everyone, considered as individuals, one at a time.
- ĉiuj - everyone, considered all together.
Each [person] must die. = Everyone must die.
That's right. But I'd also add that roboto-apokalipso is quite unnatural way to express this notion. :)
Firstly, if the second word in a compound begins with a vowel, there's no difficulty in pronouncing the roots smashed together without any helping -o- in between, so that leaves us just with robotapokalipso. Secondly, you shouldn't really make a compound here. More natural way would be to use an adjective robota or a descriptor de robotoj. But also, I couldn't really find any usage of the noun apokalipso outside the religious meaning of the last book of the New Testament. I think it still works fine as a metaphor, but I would be cautious here and suggest saying mondofino, instead.