Source: Notre Dame J. Formal Logic Volume 35, Number 3
(1994), 450-457.
This paper gives a new, purely
semantic proof of the following theorem: if an
intermediate propositional logic L has the
disjunction property then a disjunction free formula is
provable in L iff it is provable in intuitionistic logic.
The main idea of the proof is to use the well-known
semantic criterion of the disjunction property for
"simulating" finite binary trees (which characterize
the disjunction free fragment of intuitionistic logic) by
general frames.
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