1. A.E. Darbyshire (1968): Exercises in Linguistics, I Edn. P.39.
2. Bloomfield, L. (1933): Language, P. 178.
3. E.A. Nida (1949): morphology : The Descriptive Analysis of Words, II Edn., P.I.
4. Gleason, H.A. (1961) : An introduction to Descriptive Linguistics, P.51