"Strong typing vs. strong testing" [OT]

[RG]

In article 
<f15c3684-97b3-4605-a6d0-eb6b8aaf26d3 at a7g2000prb.googlegroups.com>,
 Peter Nilsson <airia at acay.com.au> wrote:

> Keith Thompson <ks... at mib.org> wrote:
> > The radian is defined as a ratio of lengths. That ratio
> > is the same regardless of the size of the circle.  The
> > choice of 1/(2*pi) of the circumference isn't arbitrary
> > at all; there are sound mathematical reasons for it.
> 
> Yes, but what is pi then?
> 
> > Mathematicians could have chosen to set the full
> > circumference to 1, for example, but then a lot of
> > computations would contain additional multiplications
> > and/or divisions by 2*pi.
> 
> The formula: circumference = 2 x pi x radius is taught
> in primary schools, yet it's actually a very difficult
> formula to prove!

What's to prove?  That's the definition of pi.

rg