can the following proposition be proved? If so please suggest a method. Can Kempe’s Argument be used for proof ?  

Proposition: A normal map has a colouring of countries by 4 colours iff the edges of the map can be properly coloured by 3 colours. 



Coloring of a normal map
I have found a proper proof in these places:


[1) Peterson Graph by D.A. Holton & J. Sheehan](http://books.google.lk/books?id=sMSOSgbCx3kC&pg=PA72&lpg=PA72&dq=Every%20bridgeless%20cubic%20planar%20graph%20is%203-edge%20colourable.&source=bl&ots=PoYmhUn8Ad&sig=5Y3h8-JadWRagoXZdbqf_lvZTKU&hl=en&sa=X&ei=yvY0VK6fOobT7Qa5g4DwCQ&ved=0CCQQ6AEwAQ#v=onepage&q=Every%20bridgeless%20cubic%20planar%20graph%20is%203-edge%20colourable.&f=false)


2) <http://www.cs.rpi.edu/~goldberg/14-GT/18-plane.pdf>


