% Graph 3-Coloring Problem
% Input: edges of a graph
edge(1,2).
edge(1,3).
edge(2,3).
edge(2,4).
edge(3,4).

% Define colors
color(red).
color(green).
color(blue).

% Each node gets exactly one color
node_color(X,C) v -node_color(X,C) :- node(X), color(C).

% Adjacent nodes must have different colors
:- edge(X,Y), node_color(X,C), node_color(Y,C).

% Define nodes
node(X) :- edge(X,_).
node(Y) :- edge(_,Y).