Abstract
In 1986 Tardos proved that for the poset 1+2+2+2+1, the clone of monotone operations is nonfinitely generated. We generalize his result in the class of series parallel posets. We characterize the posets with nonfinitely generated clones in this class by the property that they have a retract of the form either 1+2+2+2+1, 2+2+1, or 1+2+2.
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Communicated by B. A. Davey
Research partially supported by Hungarian National Foundation for Research under grant no. 1903.
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Zádori, L. Series parallel posets with nonfinitely generated clones. Order 10, 305–316 (1993). https://doi.org/10.1007/BF01108826
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DOI: https://doi.org/10.1007/BF01108826