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Nowhere-zero flows and coloring of planar graphs are related by duality. (wiki) I heard that there was a similar relation for nowhere-zero flows in signed graphs and colorings of some other graphs. I can't seem to find it. Can somebody say what the relation is and maybe also explain it?

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I do not recall seeing any duality type relation between flows and colourings in general graphs. –  Chris Godsil May 18 at 21:32
    
Sorry, I see that I left out an important word: edited! –  bart_m8 May 19 at 5:34
    
I think you might be referring to colourings of graphs embedded in the projective plane. –  nvcleemp May 19 at 6:57
    
Yes, I think that was it: embedded in the projective plasne. –  bart_m8 May 19 at 19:58

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