A new form of α-compactness is introduced in L-topological spaces by α-open L-sets and their inequality where L is a complete de Morgan algebra. It doesn’t rely on the structure of the basis lattice L. It can also be characterized by means of α-closed L-sets and their inequality. When L is a completely distributive de Morgan algebra, its many characterizations are presented and the relations between it and the other types of compactness are discussed. Countable α-compactness and the α-Lindelöf property are also researched.
The paper deals with the existence of multiple positive solutions for the boundary value problem (ϕ(p(t)u (n−1))(t))′ + a(t)f(t, u(t), u′ (t), . . . , u(n−2)(t)) = 0, 0 < t < 1, u (i) (0) = 0, i = 0, 1, . . . , n − 3, u (n−2)(0) = mP−2 i=1 αiu (n−2)(ξi), u(n−1)(1) = 0, where ϕ: R → R is an increasing homeomorphism and a positive homomorphism with ϕ(0) = 0. Using a fixed-point theorem for operators on a cone, we provide sufficient conditions for the existence of multiple positive solutions to the above boundary value problem.
We prove that it is independent of ZFC whether every Hausdorff countable space of weight less than $c$ has a dense regular subspace. Examples are given of countable Hausdorff spaces of weight $c$ which do not have dense Urysohn subspaces. We also construct an example of a countable Urysohn space, which has no dense completely Hausdorff subspace. On the other hand, we establish that every Hausdorff space of $\pi$-weight less than $\mathfrak p$ has a dense completely Hausdorff (and hence Urysohn) subspace. We show that there exists a Tychonoff space without dense normal subspaces and give other examples of spaces without “good” dense subsets.