On limit-point and separation criteria for linear differential expressions Everitt, William Norrie; Giertz, Magnus — 1973 Proceedings of Equadiff III
On the transformation theory of ordinary second-order linear symmetric differential expressions William Norrie Everitt — 1982 Czechoslovak Mathematical Journal
Some remarks on the strong limit-point condition of second-order linear differential expressions William Norrie Everitt — 1986 Časopis pro pěstování matematiky
A singular spectral identity and inequality involving the Dirichlet integral of an ordinary differential expression William Norrie Everitt; S. D. Wray — 1982 Czechoslovak Mathematical Journal
On the limit-3 classification of the square of a second-order, linear differential expression William Norrie Everitt; Magnus Giertz — 1976 Czechoslovak Mathematical Journal