a-b is not -(b-a)?

Are there any values for a and b such that a-b is not -(b-a)?

Edit: What's wrong with LaTeX here? $$≠$$

Edit 2: There's a value for a such that a≠a--NaN.

You'll have to show the TeX source for that display...

As for the main question, NaN answers it, except that NaN isn't exactly a value; it's a notation for a non-value.

$$≠$$. $$\ne$$ does it too.

1-NaN gives NaN and -(NaN-1) gives NaN. Which, in this case, kind of counts, because NaN≠NaN, but kind of not, because it's the same thing reported.

Edit: I've edited it to make it more clear what I actually want.

Yup, looks like a bug. I'm not so surprised that non-ASCII characters (such as ≠) don't work in TeX, but \ne should work. By all means complain on the Discourse forum. :~)

Oh, and mathematically there are no values of a and b that make the inequality true. I don't think there are any floating point computations either, but I won't swear to it.

TeX doesn't seem to even work on the Discourse meta-forum.

Yeah its an optional extra.

I have a feeling if there were, plenty mathematical rules would have to be questioned. Like the distributive property.

(Excluding NaN because that's not a real value)

Right, there's no question about the underlying mathematics. But floating point computer arithmetic is weird; for example, in some cases it isn't associative.