1. Ayık, G., Ayık, H., Ünlü, Y.: On semigroup presentations and Adian graphs. Discrete Math. 308(11), 2288–2291 (2008)
2. Ayık, H., Campbell, C.M., O’Connor, J.J., Ruškuc, N.: The semigroup efficiency of groups and monoids. Math. Proc. Roy. Irish Acad. 100A(2), 171–176 (2000)
3. Ayık, H., Kuyucu, F., Vatansever, B.: On semigroup presentations and efficiency. Semigroup Forum 63, 231–242 (2002)
4. Campbell, C.M., Mitchell, J.D., Ruškuc, N.: On defining groups efficiently without using Inverses. Math. Proc. Cambridge Philos. Soc 133, 31–36 (2002)
5. Higgins, P.M.: Techniques of Semigroup Theory. Oxford University Press, Oxford (1992)