## 11 April 2008

### Two quotes from Principia Mathematica (Russell and Whitehead)

"From this proposition it will follow, when arithmetical addition has been defined, that 1+1=2." -- a comment to proposition 54.43.
"The above proposition is occasionally useful." -- a comment to proposition 110.643, which proves that 1+1=2.

Quite the understatement, don't you think?

Anonymous said...

Reminds me of this: I has a mathematical system!

Veky said...

Well, not really, I'd think. How useful 1+1=2 really is? It is in elementary mathematics, but not much in general abstract math - at least not without much more algebra.

Anonymous said...

Useful? Yes. And in the same spirit.

Early on in my Algebra I course we review (it's not always review) some properties of real numbers. I like talking about closure. The kiddies usually have not heard about closure. And we talk about "proof by counterexample". I present them with evidence that the natural numbers are not closed for subtraction.

And then I ask them to 'prove' something: "Show evidence that the set {0,1} is not closed under addition"

I should thank Bertrand Rusell every time I get to that spot...

Jonathan

Anonymous said...

It's very useful in everyday life. So for all those people who carry Russell and Whitehead around at the supermarket it's certainly critical.