1. Ph. Dwinger, Generalized Post algebras, Bulletin de l'Acad�mie Polonaise des Sciences. S�rie des Sciennces Math�matiques, Astronomiques et Physiques 16 (1968), pp. 559?563.
2. Ph. Dwinger, Ideals in generalized Post algebras, ibid. 17 (1969), pp. 483?486.
3. Ng. Cat Ho, Generalised Post algebras and their applications to some infinitary many-valued logics, Dissertationes Mathematicae CVII (1973), pp. 1?76.
4. Ng. Cat Ho, A relational model of databases with context dependent null values, submitted for publication.
5. Ng. Cat Ho, Context-dependent null values and multi-valued dependencies in relational databases, Bulletin de l'Academie Polonaise des Sciences, to appear.