Does American English allow the use of "must not" instead of "can't" to say that something is believed to be logically impossible?
Please consider the following examples:
It must not be true!
How can you say such a thing? You must not be serious! (-you gotta be kidding!)
A: Joe wants something to eat.
B: But he just had lunch. He must not be hungry already.
(-it's impossible that he is hungry because he just had lunch)
I just bought a box of cereal yesterday. It must not be empty already.
You just started filling out your tax forms 10 minutes ago. You must not be finished with them already?
If A is bigger than B, and B is bigger than C, then C must not be bigger than A.