Re: Minimal Counter-example to the 4CT.


bill wrote:

In one sense, "the Minimal Counter-example to the 4CT" says that there
exists a 4-colorable planar graph, to which you can add a vertex and
get a 5-colorable planar graph.

Perhaps this is hair splitting, but a minimal counterexample to the
four color conjecture (now theorem) involves a 4-colorable planar
graph to which one adds a vertex and gets a planar graph that is
not 4-colorable.

Every 4-colorable graph is also 5-colorable.

Literally a minimal counterexample would be a planar graph that is
not 4-colorable, but in which the removal of any vertex produces a
4-colorable (necessarily planar) graph.

regards, chip

.

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