1. Ahsan, J., Thaheem, A.: On ideals in BCK-algebras. Math. Semin. Notes 5, 167–172 (1977)
2. Aslam, M., Deeba, E., Thaheem, A.: On spectral properties of BCK-algebras. Math. Japonica 38(6), 1121–1128 (1993)
3. Aslam, M., Thaheem, A.: On certain ideals in BCK-algebras. Math. Japonica 36(5), 895–906 (1991)
4. Balbes, R., Dwinger, P.: Distributive Lattices. Abstract Space Publishing (2011)
5. Birkhoff, G.: Lattice Theory. American Mathematical Society Colloquium Publications (1967)