Abstract
The notion of cycle-free partial order (CFPO) was defined by R. Warren, and the major cases of the classification of the countable sufficiently transitive CFPOs were given, the finite and infinite chain cases, by Creed, Truss, and Warren. It is the purpose of this paper to complete the classification. The cases which remained untreated were CFPOs not embedding an infinite ‘alternating chain’ ALT (which can only happen in the finite chain case). It is shown that if a k-CS-transitive CFPO does not embed ALT, where k ≥ 3, then it does not embed any alternating chain of size k + 3, and this leads to the desired classification (which is only given explicitly for k = 3 and 4). The general result says that the class of k-CS-transitive CFPOs for k ≥ 3 not embedding ALT admits a recursive classification.
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References
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Truss, J.K. On k-CS-Transitive Cycle-Free Partial Orders with Finite Alternating Chains. Order 15, 151–165 (1998). https://doi.org/10.1023/A:1006172607771
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DOI: https://doi.org/10.1023/A:1006172607771