Journal of Symbolic Logic

Unification in Intuitionistic Logic

Silvio Ghilardi

Full-text: Remote access If you are a member of the ASL, log in to Euclid for access.
Full-text is available via JSTOR, for JSTOR subscribers. Go to this article in JSTOR.


We show that the variety of Heyting algebras has finitary unification type. We also show that the subvariety obtained by adding it De Morgan law is the biggest variety of Heyting algebras having unitary unification type. Proofs make essential use of suitable characterizations (both from the semantic and the syntactic side) of finitely presented projective algebras.

Article information

J. Symbolic Logic Volume 64, Issue 2 (1999), 859-880.

First available in Project Euclid: 6 July 2007

Permanent link to this document


Mathematical Reviews number (MathSciNet)

Zentralblatt MATH identifier

Primary: 03B20: Subsystems of classical logic (including intuitionistic logic)
Secondary: 68T15: Theorem proving (deduction, resolution, etc.) [See also 03B35] 03B55: Intermediate logics 06D20: Heyting algebras [See also 03G25] 08B30: Injectives, projectives

E-Unification Projective Heyting Algebras Exact Formulas Admissible Inference Rules


Ghilardi, Silvio. Unification in Intuitionistic Logic. Journal of Symbolic Logic 64 (1999), no. 2, 859--880.

Export citation