Bounded elementary extensions of trees with unbounded paths
A tree is a partially ordered set that is downwards linear and downwards connected. A tree is called bounded when each of its paths (i.e. maximal linearly ordered subsets) contains a greatest element. In a bounded tree, each path can be defined by a first-order formula using the leaf of the path as parameter. Bounded trees can be used to model computational systems such as Zeno machines whereby the leaf of a path represents the state to which an infinitely long sequence of computations converges, or a state that is assigned to a computational sequence that loops. We identify a sufficient condition under which certain trees that are not bounded, can be elementarily embedded in trees that are bounded. Several tree operations are also given, and Feferman-Vaught style preservation properties for these operations are proved.