Gittin 25: Berera, Retroactive Clarification

The rabbis consider the concept of berera, retroactive clarification, in today's daf.  Is a man permitted to change an earlier decision based on new information?  At first the rabbis say that this is not allowed.  We learned yesterday that a man is not permitted to write a get and then later decide whether it will be presented to one or the other of his two wives.  

Is this the same as a conditional decision?  The rabbis argue that it is not.  In the case of berera, the rabbis say that a later action clarifies an earlier issue.  Conditional agreements are stated in advance: if x, then y.  

Throughout today's daf, the rabbis challenge the notion that berera is not permitted.  They use examples from Masechet Pesachim, where a father is permitted to slaughter the korban pesach on behalf of whomever arrives in Jerusalem first (whether the enthusiastic girls and the halachically lazy boys).  As they were adults, everyone was obligated to participate, but the father pretended that they had to race.

At the end of today's daf we are introduced to another example.  If a man writes and signs a get while very ill, telling his wife that the get will be enforced if and when he dies, is that get valid?  We know that gettin must be delivered before a person dies.  The rabbis seem to agree that this get is valid.  He planned and intended the get to be delivered properly in advance of his death. His wife is in possession of the get until he dies, and so she is forbidden to other men until the time of his death.  At that point she is divorced first rather than widowed first.