Yep. Completely agree with Crisc. "I will not argue with you", "Those are my final words" etc, and then walking away is the best way to end arguments.
I definitely have one of these, and it's great to know we're not alone.
I'm sorry if this is repetative as I haven't had a chance to go through all the posts. Your child acts and sounds very much like... a hypothetical person who looks and acts just like me. I'm, er, I mean 'she' is much better now, but this simple approach was very effective, along with one or two sharp consequences for not following the spirit of the rule. No claims that I, er, she didn't know were accepted because it should be obvious.
The other thing that jumps to mind is specifically talking about how certain scenarios are not about who is right and who is wrong. It is about moving forward in a functional, useful way and spending time looking backward to examine who is at fault is a waste of time. We spend very very little time at my house looking at who is at fault or wrong, except jokingly when we blame an imaginary friend we have kept around for that precise purpose.
