Looking at MacLane's thesis on proof theory in the light of combinatory logic

@article{paperbot778,
  title = {A Forgotten Theory of Proofs ?},
  author = {Erwin Engeler},
  journal = {Logical Methods in Computer Science},
  volume = {Volume 15, Issue 3},
  year = {2019},
  doi = {10.23638/lmcs-15(3:7)2019}
}