arc(1, (2; 3)).
arc(2, 3).

% Collect the vertices
vertex(X) :- arc(X, _).

% Symmetry (undirected graph)
arc(X, Y) :- arc(Y, X).

% Representation 1:
% #show red/1. #show green/1. #show blue/1.
% red(Vertex), green(Vertex), blue(Vertex) :- vertex(Vertex).
% % Remove the dupes
% :- red(V1), red(V2), V1 != V2.
% :- green(V1), green(V2), V1 != V2.
% :- blue(V1), blue(V2), V1 != V2.
% Remove the adjacent edges with same color
% :- arc(X, Y), red(X), red(Y).
% :- arc(X, Y), green(X), green(Y).
% :- arc(X, Y), blue(X), blue(Y).


% Representation 2:
% #const n = 6.

% #show color/2.   

% { color(X,1..n) } = 1 :- vertex(X).
% :- arc(X,Y), color(X,C), color(Y,C).