We prove that the c.e. Q(1)-degrees are not dense, and there exists a c.e. Q(1)-degree with no minimal c.e. predecessors. It is proved that if M-1 and M-2 are maximal sets such that M1Q1M2 then M11M2 or M21M1. We also show that there exist infinite collections of Q(1)-degrees {ai}i and {bi}i such that the following hold: (i) for every i,j, ai展开▼
