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A Problem of Normal Form in Natural Deduction |
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| Authors: | Jan von Plato |
| Abstract: | Recently Ekman gave a derivation in natural deduction such that it either contains a substantial redundant part or else is not normal. It is shown that this problem is caused by a non‐normality inherent in the usual modus ponens rule. |
| Keywords: | Natural deduction Normal form Elimination rules Sequent calculus |