Showing posts with label induction. Show all posts
Showing posts with label induction. Show all posts

Friday, March 20, 2009

Horses on Induction

Theorem. All horses are the same color.

Proof. Induct on the number of horses. Base case: 1 horse. Clearly with just 1 horse, all horses have the same color.

Now, for the inductive step: let's show that if it is true for any group of N horses, that all have the same color, then it is true for any group of N+1 horses.

Well, given any set of N+1 horses, if you exclude the last horse, you get a set of N horses. By the inductive step these N horses all have the same color. But by excluding the first horse in the pack of N+1 horses, you can conclude that the last N horses also have the same color. Therefore all N+1 horses have the same color. QED.

Q. Where is the flaw in the induction argument ?

Clue: Double - check the induction argument at a specific case, P(2) => P(3). Strong induction ?

More questions:
Is there anything else besides the above mentioned problem in the induction argument ?