Principal Solutions of Disconjugate n-th Order Linear Differential Equations

where P, (t, A) is a polynomial in A of degree n with coefficients which are real-valued, continuous functions of t on some interval I and with positive leading coefficient. Part I deals with disconjugacy criteria for (1); Part II with the definition, existence, and properties of principal solutions of disconjugate equations (1); and Part III with the existence of solutions with two-sided restrictions on their logarithmic derivatives. One result in Part I states that if P.n(t, A) has only real zeros, Al(t) ? * * n(t), and these are separated by constants cl1, * n-ly