John Randall wrote:
> Basic idea: Over time, the numbers become closer.  Since their 
> sum is constant and positive, they end up nonnegative.  It 
> suffices to show that the sum of squares eventually decreases.  
> It does on one step if x+y+z>0, but I cannot yet do the rest.

I think it suffices to focus on the cases where a negative number
combines with the largest positive number, and when the largest
positive number is greater in magnitude than any of the negative
numbers.

It can be shown that any other cases eventually lead to such
a case, except when the sequence terminates. 

-- 
Raul

 

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