--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/src/HOL/Induct/Mutil.thy Wed May 07 12:50:26 1997 +0200
@@ -0,0 +1,32 @@
+(* Title: HOL/ex/Mutil
+ ID: $Id$
+ Author: Lawrence C Paulson, Cambridge University Computer Laboratory
+ Copyright 1996 University of Cambridge
+
+The Mutilated Chess Board Problem, formalized inductively
+ Originator is Max Black, according to J A Robinson.
+ Popularized as the Mutilated Checkerboard Problem by J McCarthy
+*)
+
+Mutil = Finite +
+consts
+ domino :: "(nat*nat)set set"
+ tiling :: 'a set set => 'a set set
+ below :: nat => nat set
+ evnodd :: "[(nat*nat)set, nat] => (nat*nat)set"
+
+inductive domino
+ intrs
+ horiz "{(i, j), (i, Suc j)} : domino"
+ vertl "{(i, j), (Suc i, j)} : domino"
+
+inductive "tiling A"
+ intrs
+ empty "{} : tiling A"
+ Un "[| a: A; t: tiling A; a <= Compl t |] ==> a Un t : tiling A"
+
+defs
+ below_def "below n == nat_rec {} insert n"
+ evnodd_def "evnodd A b == A Int {(i,j). (i+j) mod 2 = b}"
+
+end