IntegerVar is the efficient, unboxed representation of an integer. (actually, it is only unboxed so long as it fits within some size limit such as 32 bits. Those IntegerVars? that exceed this limit pay their own boxing cost to store their representation on the heap. This need not concern us here.) See "The Var vs Heaper distinction." When we know that we are dealing specifically with an integer, we'd like to be able to stick with IntegerVars? without having to convert them to XuIntegers?. However, we`d like to be able to do everything that we could normally do if we had an XuInteger.