TY  - RPRT
TI  - EIGENFUNCTION EXPANSIONS FOR FORMALLY SELF-ADJOINT PARTIAL DIFFERENTIAL OPERATORS. I.
AU  - F E Browder
PY  - 1956
DO  - 10.1073/pnas.42.10.769
UR  - https://pubmed.ncbi.nlm.nih.gov/16589949/
ID  - 16589949
ER  -