In section 2.1.6 we mention a data structure used to
represent infinite objects called a *stream*, which is central to
many approaches to exact real arithmetic. Streams are infinite
sequences, and are explored in more detail in section 3.2.
Importantly, we will see that working with streams is fundamentally
different from working with finite data structures like the mantissa
of a floating point number. When using a data structure of finite
length, it is possible to examine any element of the structure at any
point. When using a stream, however, only a finite number of elements
at the head of the stream may be accessed at a given time.