On Partial Languages (Grabowski, 1981)
This paper mentions that not every poset is expressible, and that a poset shape is not expressible (not build out of duoidal expressions) if and only if it admits a full inclusion of the Z-poset shape.
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This paper mentions that not every poset is expressible, and that a poset shape is not expressible (not build out of duoidal expressions) if and only if it admits a full inclusion of the Z-poset shape.