For any 
 <A HREF = "variables.html">flexible variable</A> 
 <CODE>v</CODE>,
the expression 
 <CODE>v'</CODE>
in an 
 <A HREF = "action.html">action</A>
refers to the value of 
 <CODE>v</CODE>
in the second
   <A HREF = "states.html">state</A>
of the
 <A HREF = "step.html">step</A>.