
diff -r ff6787d730d5 -r 260090b54ef9 doc-src/Exercises/2000/a1/Hanoi.thy
--- a/doc-src/Exercises/2000/a1/Hanoi.thy	Fri Apr 29 18:13:28 2005 +0200
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,46 +0,0 @@
-(*<*)
-theory Hanoi = Main:
-(*>*)
-subsection {* The towers of Hanoi \label{psv2000hanoi} *}
-
-text {*
-
-We are given 3 pegs $A$, $B$ and $C$, and $n$ disks with a hole, such
-that no two disks have the same diameter.  Initially all $n$ disks
-rest on peg $A$, ordered according to their size, with the largest one
-at the bottom. The aim is to transfer all $n$ disks from $A$ to $C$ by
-a sequence of single-disk moves such that we never place a larger disk
-on top of a smaller one. Peg $B$ may be used for intermediate storage.
-
-\begin{center}
-\includegraphics[width=0.8\textwidth]{Hanoi}
-\end{center}
-
-\medskip The pegs and moves can be modelled as follows:
-*};  
-
-datatype peg = A | B | C
-types move = "peg * peg"
-
-text {*
-Define a primitive recursive function
-*};
-
-consts
-  moves :: "nat => peg => peg => peg => move list";
-
-text {* such that @{term moves}$~n~a~b~c$ returns a list of (legal)
-moves that transfer $n$ disks from peg $a$ via $b$ to $c$.
-Show that this requires $2^n - 1$ moves:
-*}
-
-theorem "length (moves n a b c) = 2^n - 1"
-(*<*)oops(*>*)
-
-text {* Hint: You need to strengthen the theorem for the
-induction to go through. Beware: subtraction on natural numbers
-behaves oddly: $n - m = 0$ if $n \le m$. *}
-
-(*<*)
-end
-(*>*)




