1. Data type specification
2. {ASM79} Ausiello G. and Mascari G. F. "On the Design of Algebraic Data Structures with the Approach of Abstract Data Types" Proceedings of EUROSAM 79 (Springer-Verlag Lecture Notes in Computer Science 72). {ASM79} Ausiello G. and Mascari G. F. "On the Design of Algebraic Data Structures with the Approach of Abstract Data Types" Proceedings of EUROSAM 79 (Springer-Verlag Lecture Notes in Computer Science 72).
3. {CHN65} Cohn P. M. Universal Algebra Harper and Row New York 1965 {CHN65} Cohn P. M. Universal Algebra Harper and Row New York 1965