[1] Š. Schwarz: 
A semigroup treatment of some theorems on non-negative matrices. Czechoslovak Math. J. 15 (90) (1965), 212-229. 
MR 0175919 | 
Zbl 0232.20139[2] Š. Schwarz: 
A new approach to some problems in the theory of non-negative matrices. Czechoslovak Math. J. 16 (91) (1966), 274-284. 
MR 0201452 | 
Zbl 0232.20140[3] Ю. И. Любич: 
Оценка для оптимальной детермннизации недетермннованиых автономных автоматов. Сиб. мат. ж. 5 (1964), 337-355. 
MR 0162725 | 
Zbl 1117.65300[4] В. R. Heap, M. S. Lynn: 
The structure of powers of non-negative matrices I. The index of convergence. J. SIAM Appl. Math. 14 (1966), 610-639. 
DOI 10.1137/0114052 | 
MR 0225671