Author: José de Jesús García Ruvalcaba
Date: 03:46:05 07/13/01
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On July 12, 2001 at 15:25:21, Bruce Moreland wrote: >On July 12, 2001 at 13:53:01, Dann Corbit wrote: > >>However, the previous sentence says "if and only if" and therefore it is >>required at all times. If a capture can be made, then there is an opposing side >>pawn. If a capture cannot be made there is none. I also verified the meaning >>with Steven J. Edwards. At any rate, I have asked him to change the meaning for >>the next iteration of the standard. > >If I say "A is true if B is true", A is true if B is true, and A is undefined if >B is false. > >If I say "A is true if and only if B is true", A is true if B is true, and A is >false if B is false. But if A is false, that doesn't mean that B is false, >which is what you contend. > "if and only if" is a logical equivalence, at least in math books. And in classical logic, B has to be either false or true. So if you say "A is true if and only if B is true" and A is false, then B has to be false too (because if it is true, then A has to be true and we get a contradiction). I always interpreted Edwards' words the way Dann has explained. I guess, my logic is good but my English is not (: José. [snip] >bruce
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