JCT
1998
14 years 4 days ago
1998
If P is an upper semilattice whose Hasse diagram is a tree and whose cartesian powers are Macaulay, it is shown that Hasse diagram of P is actually a spider in which all the legs ...
APAL
1998
14 years 6 days ago
1998
We consider the computably enumerable sets under the relation of Qreducibility. We first give several results comparing the upper semilattice of c.e. Q-degrees, RQ, ≤Q , under ...
APAL
2007
14 years 18 days ago
2007
Based on a result of Nies on definability the upper semilattice of computably enumerable degrees (denoted by R), we find that in R filters generated by definable subsets are al...