I want to ask C and D.
how to show that is also a metric?
I can just work out II, and only get ...maybe...s(st-ts)t=0...
why I and III are all right?
why these two curve intersect 2 points when x>0?why not 0 or 1?
Thank you very much!
If some Qs had been asked before, just reply me the link is okey~~~