1. Die Grundlehren der mathematischen Wissenschaften, Band 161;Bhatia, N. P.,1970
2. An analysis of the characteristic equation of the scalar linear difference equation with two delays;Carvalho, L. A. V.,1980
3. Pure and Applied Mathematics, Vol. XXI;Hale, Jack K.,1969
4. Applied Mathematical Sciences, Vol. 3;Hale, Jack,1977
5. Some stability theorems for ordinary difference equations;Hurt, James;SIAM J. Numer. Anal.,1967