Add at least one example of Sub-Clock Conversion Operators applied to clocked expressions

[casella]

In Section 16.5.2, 5 sub-clock conversion operators are defined, all taking an input u which is defined as

The input argument u is a clocked expression or an expression of type Clock.

All the examples of the four operators subSample(), superSample(), shiftSample() and backSample() always have a Clock expression as input. I think it would be good to show at least one case where the input is actually a clocked expression.