Contractible n-Manifolds and the Double n-Space Property

We are interested in contractible n-manifolds M which "split" as M = A union B where A,B, and A intersect B are all homeomorphic to Euclidean n-space (such M are called open n-splitters) or A,B, and A intersect B are all homeomorphic to the n-dimensional unit ball (such M are called closed n-splitters). We introduce a closed 4-splitter M from which we construct an infinite collection of distinct closed 4-splitters and an uncountable set of open 4-splitters.