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alas, alas! that is exactly what i tried... let me think:
(P1) A is necessary for B
this means "if not A, then not B"... i visualize this as B<A, where "<" means "contained in"
(P2) B, unless C
this means "if not C, then B"... which equals "if not B, then C"... i visualize this as B and C intersecting each other
(P3) A is sufficient for D
this means "if A then D"... i visualize this as A<D
(Q1) D unless A... this means A can be true while D is false... which is in contradiction with P1
(Q3) C unless D... we can have C true, D false; C true, D true; C true, D false, but not C false and D false... lets see... if not C (C false), by P2, then B... if B, by P1, then A... if A, by P3, then D...
i would now vote for (3) AND (4)... (they are equivalent, arent they?)
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