H. Frentzen

On the commutativity of certain quasi-differential expressions II

A. Zettl, D. Race, H. Frentzen, 1993, Proceedings of the Royal Society of Edinburgh: Section A Mathematics.

Limit-Point Criteria For Not Necessarily Symmetric Ordinary Differential Expressions

H. Frentzen, 1991 .

Equivalence, adjoints and symmetry of quasi-differential expressions with matrix-valued coefficients and polynomials in them

H. Frentzen, 1982, Proceedings of the Royal Society of Edinburgh: Section A Mathematics.

ON THE LEFT-DEFINITENESS OF S-HERMITIAN SYSTEMS OF DIFFERENTIAL EQUATIONS

H. Frentzen, 1979 .

A LIMIT-POINT CRITERION FOR REAL POLYNOMIALS IN SYMMETRIC QUASI-DIFFERENTIAL EXPRESSIONS OF ARBITRARY ORDER

H. Frentzen, 1982 .