1. Ein Gegenstück zum Ritz'schen Verfahren;Trefftz,1926
2. A problem arising in the solution of the biharmonic equation;Rafal'son;Dokl. Akad. Nauk SSSR,1949
3. Trefftz's variational method for the equation ▽4u = f;Birman;Dokl. Akad. Nauk SSSR,1955
4. Variational methods of solving boundary value problems similar to the Trefftz method;Birman;Vest. Len. gos. un-ta, Seriya matem mekh. i astr.,1956