Conceptually, an interior node is an array of *n* pointers and *n - 1*
key values. A pointer is between the two key values that bound the
entries that it covers; we imagine that the array is bounded by key values
of *- &infin* and *&infin*. (In practice, two arrays, pointers and
key values, may be used since they are of different types.)

Binary search of the array of key values can be used to find the right
pointer to follow. If we have the sequence

*key _{i} pointer_{i} key_{i+1}*