Normalization of N-Graphs via Sub-N-Graphs

Alves presented in his PhD thesis a normalization procedure for N-Graphs, a multiple conclusion natural deduction for propositional classical logic proposed by de Oliveira in 2001, with proofs as directed graphs. Here we develop a new normalization for N-Graphs inspired by A. Carbones work in 1999, where she proposed a combinatorial model to study the evolution of proofs during the procedure of cut elimination.