On Mon, 29 Jul 2013, Fool wrote:

On 29/07/2013 6:20 PM, Ørjan Johansen wrote:
On Mon, 29 Jul 2013, Fool wrote:

The sentences in question are not directly self-referential or even
mutually-referential. This is more of a Curry-flavoured confused
deputy, with rule 2337 as the deputy. It says that the author can
destroy a promise with notice IFF the sentence in its "destruction by
author condition" slot is true. So:

- Sentence A: I can do Y.
- Sentence B: IF (I can do X), THEN (Z is true).
- Rule 2337 says that (I can do X) IFF (sentence A is true)
- Rule 2337 says that (I can do Y) IFF (sentence B is true)

The way I read it Rule 2337 implies IF, not IFF.

One clause says IF. Another clause secures promise destruction, and there's no other instrument allowing it, so ONLY IF.

I think if you are going to prove it's constructively valid, you need to be more precise on that point. (Not that I've checked yet whether it works with either IFF or just IF.)

I think constructively securing acts as "if not explicitly permitted, then not possible". Which means it's (IF x THEN y) AND (IF (NOT x) THEN (NOT y)), which I think is _not_ constructively equivalent to x IFF y.


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