% c-colorability by Ilkka Niemelä 
%
% requires the graph as facts vertex(.) and arc(.,.)
% Usage, e.g.,  
% UNIX> graph -ladder 40 2 | cat color.lp - | lparse -1 -c c=3 -d none | smodels 1 
% Note graph needs SGB libraries
% Using the available graphs 
% UNIX> cat color.lp graphs/p300 | lparse -1 -c c=4 -d none | smodels 

color(V,C):-  vertex(V), col(C), not othercolor(V,C).
othercolor(V,C) :- vertex(V), col(C),  col(C1), C != C1,  color(V,C1).

:- arc(V1,V2), col(C), color(V1,C), color(V2,C).


col(1..c).