src/HOL/Induct/Mutil.thy
 changeset 3120 c58423c20740 child 3424 bf466159ef84
```     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
```