If (X ′, τ ′,≤′) is an ordered compactification of the partially ordered topological space (X, τ,≤) such that ≤′ is the smallest order that renders (X ′, τ ′,≤′) a T2-ordered compactification of X, then X ′ is called a Nachbin(or order-strict) compactification of (X, τ,≤). If (X ′, τ ′,≤∗) is a finite-point ordered compactification of (X, τ,≤), the Nachbin order ≤′ for (X ′, τ ′) is described i...

We construct compact examples of D-manifolds for type IIB strings. The construction has a natural interpretation in terms of compactification of a 12 dimensional ‘F-theory’. We provide evidence for a more natural reformulation of type IIB theory in terms of Ftheory. Compactification of M-theory on a manifold K which admits elliptic fibration is equivalent to compactification of F-theory on K ×S...