Universal Regressive Isols
Joseph Barback · Proceedings of the American Mathematical Society · 1972
E. Ellentuck introduced universal isols in Math. Z. 98 (1967), 1-8, to show how counterexamples in the arithmetic of the isols may be obtained in a uniform manner. Also Ellentuck was the first to prove, in unpublished notes, that there will be regressive isols that are universal. The present paper contains a relatively short proof that every infinite multiple-free regressive isol will be universal.