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by jbaber 409 days ago
"Almost all" in math can mean "except at every integer or fraction" :)
4 comments

> "Almost all" in math can mean "except at every integer or fraction" :)

I am a mathematician, but, even so, I think that this is one of those instances where we have to admit that we have mangled everyday terminology when appropriating it, and so non-measure theoretic users should just ignore our definition. (Similarly with "group," where, at the risk of sounding tongue-in-cheek because it's so obvious, if I were trying to analyze how people usually understand its everyday meaning I wouldn't include the requirement that every element have an inverse.)

I would expect almost NO numbers are rational (integer or fraction) with an infinite number of Reals between each.
> I would expect almost NO numbers are rational (integer or fraction) with an infinite number of Reals between each.

You're right (technically correct, which is the best etc.)! That is why "almost all" can mean everything except rational numbers.

in between any two real numbers, there is a rational number, and vice versa.
And yet somehow there are infinity times more reals than rationals...

Very hard to get your head around!

An fun, immediate, horrifying, consequence.

If I remove n elements from R, the remainder has n+1 connected components.

The complement of Z in R has |Z| connected components.

The complement of Q in R has |R| connected components.

The semantics are almost always reasonable: https://en.wikipedia.org/wiki/Almost_all
Sure but that’s because 100% of real numbers, by any standard measure, aren’t integers or fractions. It bothers me if it’s used to mean 95% of something though.