Bulletin of the Section of Logic, Tome 44 (2015) no. 1-2
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French, Rohan; Humberstone, Lloyd. An Observation Concerning Porte’s Rule in Modal Logic. Bulletin of the Section of Logic, Tome 44 (2015) no. 1-2. http://geodesic.mathdoc.fr/item/BSL_2015_44_1-2_a0/
@article{BSL_2015_44_1-2_a0,
author = {French, Rohan and Humberstone, Lloyd},
title = {An {Observation} {Concerning} {Porte{\textquoteright}s} {Rule} in {Modal} {Logic}},
journal = {Bulletin of the Section of Logic},
year = {2015},
volume = {44},
number = {1-2},
url = {http://geodesic.mathdoc.fr/item/BSL_2015_44_1-2_a0/}
}
TY - JOUR
AU - French, Rohan
AU - Humberstone, Lloyd
TI - An Observation Concerning Porte’s Rule in Modal Logic
JO - Bulletin of the Section of Logic
PY - 2015
VL - 44
IS - 1-2
UR - http://geodesic.mathdoc.fr/item/BSL_2015_44_1-2_a0/
ID - BSL_2015_44_1-2_a0
ER -
%0 Journal Article
%A French, Rohan
%A Humberstone, Lloyd
%T An Observation Concerning Porte’s Rule in Modal Logic
%J Bulletin of the Section of Logic
%D 2015
%V 44
%N 1-2
%U http://geodesic.mathdoc.fr/item/BSL_2015_44_1-2_a0/
%F BSL_2015_44_1-2_a0
It is well known that no consistent normal modal logic contains (as theorems) both ◊A and ◊¬A (for any formula A). Here we observe that this claim can be strengthened to the following: for any formula A, either no consistent normal modal logic contains ◊A, or else no consistent normal modal logic contains ◊¬A.
