296 research outputs found

    Chromatic number of the product of graphs, graph homomorphisms, Antichains and cofinal subsets of posets without AC

    Full text link
    We have observations concerning the set theoretic strength of the following combinatorial statements without the axiom of choice. 1. If in a partially ordered set, all chains are finite and all antichains are countable, then the set is countable. 2. If in a partially ordered set, all chains are finite and all antichains have size ℵα\aleph_{\alpha}, then the set has size ℵα\aleph_{\alpha} for any regular ℵα\aleph_{\alpha}. 3. CS (Every partially ordered set without a maximal element has two disjoint cofinal subsets). 4. CWF (Every partially ordered set has a cofinal well-founded subset). 5. DT (Dilworth's decomposition theorem for infinite p.o.sets of finite width). 6. If the chromatic number of a graph G1G_{1} is finite (say k<ωk<\omega), and the chromatic number of another graph G2G_{2} is infinite, then the chromatic number of G1×G2G_{1}\times G_{2} is kk. 7. For an infinite graph G=(VG,EG)G=(V_{G}, E_{G}) and a finite graph H=(VH,EH)H=(V_{H}, E_{H}), if every finite subgraph of GG has a homomorphism into HH, then so has GG. Further we study a few statements restricted to linearly-ordered structures without the axiom of choice.Comment: Revised versio
    • …
    corecore