Matthias Baaz Christian G. Fermüller A Note on the Proof-Theoretic Strength of a Single Application of the Schema of Identity. 38-48 2001 conf/dagstuhl/2001ptcs Proof Theory in Computer Science http://link.springer.de/link/service/series/0558/bibs/2183/21830038.htm db/conf/dagstuhl/ptcs2001.html#BaazF01