It *is* a typo/laziness. I was meaning .9 recurring for every instance of .999 (likewise .3 recurring and .6 recurring).. I'd have put a bar above it, but I have no idea how to do that with HTML :P

I could have been clearer I suppose, but c'mon, I did do TEE maths, I know that 1/3 = .3 recurring and not .3330 :)

And yes, you're right, it is a proof not a postulation.