1. Ackermann, W.: Begründung einer strengen implikation. J. Symbolic Logic 2(21), 113–128 (1956)
2. Cano-Jorge, F.: Logical relevance in paraconsistent connexive logics I, unpublished typescript
3. Cano-Jorge, F., Estrada-González, L.: Mortensen logics. In: Indrzejczak, A., Zawidzki, M. (eds.) 10th International Conference on Non-Classical Logic. Theory and Applications (NCL 2022), vol. 358, pp. 189–201. EPTCS (2022)
4. Church, A.: The weak theory of implication. In: Burge, T., Enderton, H. (eds.) The Collected Works of Alonzo Church, chap. 8, pp. 307–318. MIT-Press, Massachusetts and London (2019). Originally published in Kontrolliertes Denken: Untersuchungen zum Logikkalkül und zur Logik der Einzelwissenschaften (Festschrift für Wilhelm Britzelmayr), edited by Albert Menne, Alexander Wilhelmy and Helmut Angstl, rotaprint, Kommissions-Verlag Karl Alber, Munich, 1951, pp. 22–37
5. Dunn, J.M.: Star and Perp: two treatments of negation. Philos. Perspect. 7, 331–357 (1993)