Why is it hardly relevant? Booleans are, per definition, 0 and 1.
So in BM, Not(not x) IS equal to x for the set of booleans which is {0,1}
The point was precisely that there is no such thing as a boolean type in BlitzMaxSo in BM, Not(not x) IS equal to x for the set of booleans which is {0,1}
(just like in C/C+) which is the reason why both expressions are different. For 2 expressions to be equivalent, you must for each possible of input values, have the same output values. Here you don't.
I thought this was illustrative of the SSwift's issue, because this is the very same problem : the input values don't lie in the {0, 1} set (that 10 there) so we're not in strict boolean logic anymore, hence the irrelevancy of your remark here. If we were using true booleans, the initial problem he pointed couldn't indeed arise.
@SSwift: you're right, this can be confusng, and having a true boolean type is desirable. There's a good reason to have a true boolean type in languages like C#. But it's realtively easy to live without.