From a406cb43bd905a550c426963e595f8c82b5e8bcb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Patrick=20L=C3=BChne?= <patrick@luehne.de>
Date: Sun, 8 Apr 2018 20:28:04 +0200
Subject: [PATCH] Update graph coloring example with placeholders

This replaces the former graph coloring example with a new formulation
that makes use of the newly supported placeholders.
---
 examples/graph-coloring.lp | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

diff --git a/examples/graph-coloring.lp b/examples/graph-coloring.lp
index 8b7487c..de5d382 100644
--- a/examples/graph-coloring.lp
+++ b/examples/graph-coloring.lp
@@ -1,12 +1,9 @@
-colored(V, red) :- vertex(V), not colored(V, green), not colored(V, blue).
-colored(V, green) :- vertex(V), not colored(V, red), not colored(V, blue).
-colored(V, blue) :- vertex(V), not colored(V, red), not colored(V, green).
+#external color(1).
+#external edge(2).
+#external vertex(1).
+#show color/2.
 
-:- edge(V1, V2), colored(V1, C), colored(V2, C).
-
-vertex(a).
-vertex(b).
-vertex(c).
-
-edge(a, b).
-edge(a, c).
+{color(V,C)} :- vertex(V), color(C).
+covered(V) :- color(V, _).
+:- vertex(V), not covered(V).
+:- color(V1,C), color(V2,C), edge(V1,V2).