Yevamot 93: The Existence of the Things That Do Not Yet Exist

First, a brief comment on Daf 91: the reading of the woman's get. Next: Establishing a vow or acquiring something that is not yet in existence in the world, which seems like R. Akiva's position. Except that R. Nachman bar Yitzchak presents a contradictory opinion in the name of R. Akiva himself (after a long chain of names of Tannaim). Which leads to other examples of treating that which does not yet exist as if it exists - where the halakhah is upheld. Which leads to a dream, as an explainer. Really. Also, when it comes to one witness to the death of a woman's husband that she's allowed to remarry - is that because the likelihood of lying in such a situation is unlikely or to enable her to marry... Plus, she'll investigate carefully because of the implications for herself. In which case, what would that testimony do for yibum? What if she especially likes her brother-in-law? Can we still assume there's no lie here?