Let $A$ be a bounded sublattice of the bounded lattice $(X,\le)$ with
$$\max A=\max X, ~~\min A=\min X$$
Let $a,b\in X$ be complements and $a\in A$.
Is $b\in A$?
Let $A$ be a bounded sublattice of the bounded lattice $(X,\le)$ with
$$\max A=\max X, ~~\min A=\min X$$
Let $a,b\in X$ be complements and $a\in A$.
Is $b\in A$?
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Counterexample: let $X=\{\emptyset,\{a\},\{b\},\{a,b\}\}$ (where $a\ne b$), and let $A=\{\emptyset,\{a\},\{a,b\}\}$. Then $X$ is a bounded lattice; $A$ is a bounded sublattice with the same $0$ and $1$; $\{a\},\{b\}$ are complements in $X$; $\{a\}\in A$, but $\{b\}\notin A$.