| Paragraph 1 | It is clear then that in the first figure all problems except the universal affirmative are proved per impossibile. |
| Paragraph 2 | When A belongs to some B, suppose that A belongs to no B, and let A belong to all C. |
| Paragraph 3 | Again suppose that A belongs to some B, and let A belong to no C. |
| Paragraph 4 | When A does not belong to an B, suppose it does belong to all B, and to no C. |
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created 1996/11/25 modified 2009/04/26