TY  - RPRT
TI  - Principal Quadratic Functionals and Self-Adjoint Second-Order Differential Equations.
AU  - W Leighton
PY  - 1949
DO  - 10.1073/pnas.35.4.192
UR  - https://pubmed.ncbi.nlm.nih.gov/16588881/
ID  - 16588881
ER  -