A newbie here, Bth advanced Maths and Forum,

Can anyone point me to a resource that has test cases for difficult to colour planar graphs that make coloring with four colors difficult. I have an idea that may demonstrate a simple proof for this theorem, however I need to find hard examples to see if I can color them with an algorithm I have developed, to see if hard problems cause the method to end up running into exponentially long solutions, if so the theorem may be incorrect

Ideally the problems will use the node and vertex graph representation such that I can print them on a page.

Thanks in Advance
TonyM