Hence N0(L) is a sublattice of N(L). Since N(L) is distributive, we have that
N0(L) is also distributive. Clearly, [0]∗ is the greatest element of N(L). Now for
any [x]∗ ∈ N0(L), we get [x]∗∩[0]∗ = [x∨0]∗ = [x]∗ and [x]∗∨ [0]∗ = [x∧0]∗ = [0]∗.
It shows that [0]∗ is the greatest element in N0(L). Now, it remains to prove the
final condition of the theorem. Assume N0(L) has the smallest element, say [d]∗
where d ∈ L. Suppose x ∈ [d]∗. Then x ∧ d = 0. Since [d]∗ is the least element,
we get [x]∗ = [x]∗∨ [d]∗ = [x ∧ d]∗ = [0]∗ = L. Hence x = 0. Thus [d]∗ = (0].
Therefore d is a dense element in L.
Hence N0(L) is a sublattice of N(L). Since N(L) is distributive, we have thatN0(L) is also distributive. Clearly, [0]∗ is the greatest element of N(L). Now forany [x]∗ ∈ N0(L), we get [x]∗∩[0]∗ = [x∨0]∗ = [x]∗ and [x]∗∨ [0]∗ = [x∧0]∗ = [0]∗.It shows that [0]∗ is the greatest element in N0(L). Now, it remains to prove thefinal condition of the theorem. Assume N0(L) has the smallest element, say [d]∗where d ∈ L. Suppose x ∈ [d]∗. Then x ∧ d = 0. Since [d]∗ is the least element,we get [x]∗ = [x]∗∨ [d]∗ = [x ∧ d]∗ = [0]∗ = L. Hence x = 0. Thus [d]∗ = (0].Therefore d is a dense element in L.
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