  In general proof theory there are two approaches to the question of identity
criteria for proofs. The first approach, which stems from Prawitz, Kreisel and
Lambek, and is based on normalization of proofs, gives good results in
intuitionistic, but not in classical logic. The second approach, which stems
from Lambek, Mac Lane and Kelly, and is inspired by the generality of proofs,
seems to be more promissing in classical logic.
