Let R be a (skew) integral domain. For 0 ≠ a ∈ R, a is simple if the interval [ aR, R ] of principal right ideals of R containing aR is not the union of two proper subintervals of [ aR, R ]. It is ...
Proceedings of the National Academy of Sciences of the United States of America, Vol. 1, No. 6 (Jun. 15, 1915), pp. 374-381 (8 pages) ...