src/HOL/Induct/Mutil.thy
 author paulson Fri, 06 Jun 1997 10:47:16 +0200 changeset 3424 bf466159ef84 parent 3120 c58423c20740 child 5931 325300576da7 permissions -rw-r--r--
Tidying and simplification of declarations
```
(*  Title:      HOL/Induct/Mutil
ID:         \$Id\$
Author:     Lawrence C Paulson, Cambridge University Computer Laboratory

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    == {i. i<n}"
evnodd_def "evnodd A b == A Int {(i,j). (i+j) mod 2 = b}"

end
```