Let 
be a set of streams of the same type. Having the
same type can be defined as follows:
Let 
and 
. Then
So the stream set is one with the property that:
In other words, the range of each channel is the same for each element
of . Intuitively, the set represents streams from a
given domain source, for example, it may be the set of possible Auslan
signs. Note that not all elements of are the same length -
i.e. the duration (in frames) isn't necessarily the same.