1. Direct decompositions;Baer, Reinhold;Trans. Amer. Math. Soc.,1947
2. American Mathematical Society Colloquium Publications, Vol. XXV;Birkhoff, Garrett,1961
3. On factors without centres in direct decompositions of groups;Golowin, O. N.;Rec. Math. N. S. [Mat. Sbornik],1939
4. Notre Dame Mathematical Lectures, no. 5;Jónsson, Bjarni,1947
5. A note on the Schmidt-Remak theorem;Kiokemeister, Fred;Bull. Amer. Math. Soc.,1947