"the wife of the dead one shall not be outside to a strange man": What is the intent of this? Because it was ruled: Yibum obtains with the wife of one but not with the "wife" of two (see above), I might think that she (the woman in the above instance) is (entirely) exempt. It is, therefore, written "the wife of the dead one shall not be outside to a strange man." What is to be done?
She undergoes chalitzah (yibum release) but not yibum. If one gives a get (to his yevamah), he forbids her to himself and to his brothers. I might think that she is (entirely) exempt, and that this follows, viz.: If chalitzah, which does not exempt a woman (from the marriage tie) exempts her from the yibum tie, then get, which does exempt a woman (from the marriage tie), how much more so should it exempt her from the yibum tie!
It is, therefore, written "the wife of the dead one shall not be outside to a strange man" — except by chalitzah. If one makes a ma'amar in his yevamah, he acquires her for himself and forbids her to the brothers. I might think that the ma'amar consummates the union. It is, therefore, written "her yavam shall come upon her" — Cohabitation consummates, and not ma'amar.