[FOM] strange phenomenon

[Sara Negri]

Dear FOMers,

May I draw your attention to the article by Jan von Plato,
"A problem of normal form in natural deduction," in Mathematical Logic
Quarterly, vol. 46 (2000), pp. 121-124. This paper shows that the problem
about -(P <-->  -P) stems from the modus ponens rule and gives a normal
derivation with the general implication elimination rule that Tennant
mentions.

Best regards,

                 Sara Negri


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Dr. Sara Negri
Department of Philosophy
Siltavuorenpenger 20 A
00014 University of Helsinki
Helsinki, Finland

fax  +358-9-19129229

tel.  +358-9-19129220

home page:
     http://www.helsinki.fi/filosofia/filo/henk/negri.htm