There is a "Meta Birkhoff Theorem" by Andreka, Nemeti and Sain (1982).5
Peter Burmeister (1993). "Partial algebras—an introductory survey". In Ivo G. Rosenberg; Gert Sabidussi (eds.). Algebras and Orders. Springer Science & Business Media. pp. 1–70. ISBN 978-0-7923-2143-9. 978-0-7923-2143-9 ↩
George A. Grätzer (2008). Universal Algebra (2nd ed.). Springer Science & Business Media. Chapter 2. Partial algebras. ISBN 978-0-387-77487-9. 978-0-387-77487-9 ↩
Foulis, D. J.; Bennett, M. K. (1994). "Effect algebras and unsharp quantum logics". Foundations of Physics. 24 (10): 1331. Bibcode:1994FoPh...24.1331F. doi:10.1007/BF02283036. hdl:10338.dmlcz/142815. S2CID 123349992. /wiki/Bibcode_(identifier) ↩