1. Disconjugacy;Coppel,1971
2. Minors of the Wronskian of the differential equation Lny + p(x)y = 0;Elias,1987
3. Nonoscillation, Disconjugacy and Integral Inequalities;Friedland;Memoirs Amer. Math. Soc.,1976
4. Uniqueness of linear boundary value problems for differential systems;Gingold;Pacific J. Math.,1978