1. Don't eliminate cut;Boolos;J. Philos. Logic,1984
2. The undecidability of k-provability;Buss;Ann. Pure Appl. Logic,1991
3. Interpolants, cut elimination and flow graphs for the propositional calculus;Carbone;Ann. Pure Appl. Logic,1997
4. Some combinatorics behind proofs;Carbone,1995
5. Cycling in proofs and feasibility;Carbone,1998