context: Two young men are on a vast, level expanse of grass, and the man in the red shirt is catching the white Frisbee.
hypothesis: Chances are about even that there are other people playing with them.
valid_hypothesis: Chances are about even that there are other people playing with them.
invalid_hypothesis: It is highly unlikely that there are other people playing with them.
hypothesis_assertion: There are other people playing with them.