TY  - RPRT
TI  - On Self-Adjoint Differential Equations of Second Order.
AU  - W Leighton
PY  - 1949
DO  - 10.1073/pnas.35.11.656
UR  - https://pubmed.ncbi.nlm.nih.gov/16578321/
ID  - 16578321
ER  -