Call a poset $X$ Dedekind-complete iff for all non-empty sets $A \subseteq X$, the following are equivalent.
- $A$ has an upper bound
- $A$ has a least upper bound.
Supposing $X = (X, \leq)$ is Dedekind-complete, is $X^\mathrm{op} = (X,\geq)$ necessarily Dedekind complete?
Yes, the infimum can be characterized as the supremum of the lower bounds, and conversely.