Example 1: 
 
   > f=sin(x);
 
   > f;
 
   sin(x)
 
   > rename(x,y);
 
   > f;
 
   sin(y)
 
 
 
Example 2: 
 
   > a=1;
 
   > f=sin(x);
 
   > rename(x,a);
 
   > a;
 
   a
 
   > f;
 
   sin(a)
 
 
 
Example 3: 
 
   > verbosity=1!;
 
   > f=sin(x);
 
   > rename(y, z);
 
   Warning: the current free variable is named "x" and not "y". Can only rename the free variable.
 
   The last command will have no effect.
 
   > rename(_x_, z);
 
   Information: the free variable has been renamed from "x" to "z".
 
 
 
Example 4: 
 
   > verbosity=1!;
 
   > rename(x,y);
 
   Information: the free variable has been named "y".
 
   > isbound(x);
 
   false
 
   > isbound(y);
 
   true