On the Embeddability of Partially Ordered Halfrings Michael BleicherSamuel Bourne Indiana University Mathematics Journal 1965 text pdf 10.1512/iumj.1965.14.14009 10.1512/iumj.1965.14.14009 en Indiana Univ. Math. J. 14 (1965) 109 - 116 state-of-the-art mathematics http://iumj.org/access/