Richard Grevers wrote:
There is a mathematical proof that you need no more
than four colours to
colour in a map so that no two adjacent areas have the same colour.
As with all mathematical proofs of facts in the real world,
you first have to check that the mathematical model applies.
In the case of the countries of the world, it does not.
If each country were contiguous, /then/ it would work.
I'm still used to maps where the former British
Empire is shaded pink and
the former French Empire is lilac :-)
Go back in time a bit and imagine a world with 5 colonial empires,
with neighbouring empires to be given different colours.
Suppose that each empire owns most of a certain corner of the globe.
But each empire also has a colony inside each of the other 4 empires.
Then they will all border each other and must all have different colours.
-- Toby