For any
 <A HREF = "state-function.html">state function</A>
 <CODE>v</CODE>, 
we define
 <CODE>v'</CODE>
to be the expression obtained by priming all the 
 <A HREF = "variables.html">flexible variables</A> 
in 
 <CODE>v</CODE>.
In other words,
   <CODE>v'</CODE>
is the expression obtained by replacing every
 <A HREF = "variables.html">flexible variable</A> 
 <CODE>z</CODE>
occurring in <CODE>v</CODE> with <CODE>z'</CODE>.