As sure as eggs is eggs
The colloquial expression as sure as eggs is eggs, meaning absolutely certain, probably comes from the mathematical expression x = x.
It's hard to argue against such an expression. If I were to take place in a debate I wouldn't fancy fighting the corner for eggs ain't eggs.
But then I am not a child. When some researchers asked a 12 year old girl to explain what was meant by '3 = 3' she told them it was incomplete and suggested that perhaps it means '3 minus 0 = 3'.
So eggs ain't eggs after all – eggs with no eggs taken away is eggs.
And that's as sure as eggs is eggs.