1. On self-adjoint domains of second order differential operators in limit-circle case;Cao;Acta Math. Sinica (N.S.),1985
2. On self-adjoint extensions in the limit-circle case of differential operators of order n;Cao;Acta Math. Sinica,1985
3. Self-adjoint operators generated by symmetric quasi-differential expressions;Cao;Acta Sci. Natur. Univ. NeiMongol,1986
4. Ordinary Differential Operators;Cao,1987
5. Theory of Ordinary Differential Equations;Coddington,1955