On the Admissible Rules of Intuitionistic Propositional Logic
Rosalie Iemhoff

Abstract:
We present a basis for the admissible rules of intuitionistic propositional
logic. Thereby a conjecture by de Jongh and Visser is proved. We also 
present a proof system for the admissible rules, and give semantic criteria
for admissibility. We use and connect all this with work on admissible
rules by Ghilardi.