Gittin 82 - Get is Complete Severance
To be effective, a Get must totally sever the marital relationship between the husband and the wife.
If one divorces his wife and says to her, "You are hereby permitted to any man but so-and-so", she is not divorced. What should he do? He should take the Get from her and give it to her again, and say to her, "You are hereby permitted to any man."
But if he wrote this restriction into the Get itself, although he later erased it, the Get is invalid, since it never was a "document of severance."