1.1 --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
     1.2 +++ b/src/HOL/Induct/Mutil.thy	Wed May 07 12:50:26 1997 +0200
     1.3 @@ -0,0 +1,32 @@
     1.4 +(*  Title:      HOL/ex/Mutil
     1.5 +    ID:         $Id$
     1.6 +    Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
     1.7 +    Copyright   1996  University of Cambridge
     1.8 +
     1.9 +The Mutilated Chess Board Problem, formalized inductively
    1.10 +  Originator is Max Black, according to J A Robinson.
    1.11 +  Popularized as the Mutilated Checkerboard Problem by J McCarthy
    1.12 +*)
    1.13 +
    1.14 +Mutil = Finite +
    1.15 +consts
    1.16 +  domino  :: "(nat*nat)set set"
    1.17 +  tiling  :: 'a set set => 'a set set
    1.18 +  below   :: nat => nat set
    1.19 +  evnodd  :: "[(nat*nat)set, nat] => (nat*nat)set"
    1.20 +
    1.21 +inductive domino
    1.22 +  intrs
    1.23 +    horiz  "{(i, j), (i, Suc j)} : domino"
    1.24 +    vertl  "{(i, j), (Suc i, j)} : domino"
    1.25 +
    1.26 +inductive "tiling A"
    1.27 +  intrs
    1.28 +    empty  "{} : tiling A"
    1.29 +    Un     "[| a: A;  t: tiling A;  a <= Compl t |] ==> a Un t : tiling A"
    1.30 +
    1.31 +defs
    1.32 +  below_def  "below n    == nat_rec {} insert n"
    1.33 +  evnodd_def "evnodd A b == A Int {(i,j). (i+j) mod 2 = b}"
    1.34 +
    1.35 +end