Comments on: SICP section 2.2.1 http://eli.thegreenplace.net/2007/08/10/sicp-section-221/ Eli Bendersky's personal website Fri, 21 Nov 2008 22:27:20 +0000 http://wordpress.org/?v=2.6.2 By: eliben http://eli.thegreenplace.net/2007/08/10/sicp-section-221/#comment-101442 eliben Sat, 26 Jan 2008 10:15:32 +0000 http://eli.thegreenplace.net/2007/08/10/sicp-section-221/#comment-101442 Hi Sergey, You're right, I did a mistake in my call tree, hence the proof is incorrect. If you have an idea for a complete proof, let me know. Hi Sergey,
You’re right, I did a mistake in my call tree, hence the proof is incorrect.
If you have an idea for a complete proof, let me know.

]]> By: Sergey Khenkin http://eli.thegreenplace.net/2007/08/10/sicp-section-221/#comment-101438 Sergey Khenkin Sat, 26 Jan 2008 09:36:31 +0000 http://eli.thegreenplace.net/2007/08/10/sicp-section-221/#comment-101438 Hi Eli, I like your website very much. The effort you did is really outstanding! Keep up great work. I want to comment on exercise 2.19. The idea for a proof of the fact that the order of the list coin-values does not affect the answer of cc is very nice but the proof is not correct because actually the call tree should look like this: <code> (N, (a b c d)) |->(N, (b c d)) |--|->(N, (c d)) |--|->(N-b, (b c d)) |->(N-a, (a b c d)) |--|->(N-a, (b c d)) |--|->(N-a-a, (a b c d)) </code> So it is not symmetric for a and b unfortunately :( Hi Eli,
I like your website very much. The effort you did is really outstanding! Keep up great work.

I want to comment on exercise 2.19. The idea for a proof of the fact that the order of the list coin-values does not affect the answer of cc is very nice but the proof is not correct because actually the call tree should look like this:

(N, (a b c d))
|->(N, (b c d))
|--|->(N, (c d))
|--|->(N-b, (b c d))
|->(N-a, (a b c d))
|--|->(N-a, (b c d))
|--|->(N-a-a, (a b c d))

So it is not symmetric for a and b unfortunately :(

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