On coherent systems of projections for aleph_1 separable groups
Paul C. Eklof, Alan H. Mekler, Saharon Shelah · arXiv (Cornell University) · 1993
It is proved consistent with either CH or the negation of CH that there is an aleph_1-separable group of cardinality aleph_1 which does not have a coherent system of projections. It had previously been shown that it is consistent with not CH that every aleph_1-separable group of cardinality aleph_1 does have a coherent system of projections.